Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

A recent report on the detection of very-high-energy gamma rays from V4641 Sagittarii (V4641 Sgr) up to  ≈0.8 PeV has made it the second confirmed “PeVatron” microquasar. Here we report on the observation of V4641 Sgr with X-Ray Imaging and Spectroscopy Mission (XRISM) in 2024 September. Thanks to the large field of view and low background, the CCD imager Xtend successfully detected for the first time X-ray extended emission around V4641 Sgr with a significance of ≳4.5σ and >10σ based on our imaging and spectral analysis, respectively. The spatial extent is estimated to have a radius of 7′ ± 3′ (13 ± 5 pc at a distance of 6.2 kpc) assuming a Gaussian-like radial distribution, which suggests that the particle acceleration site is within ~10 pc of the microquasar. If the X-ray morphology traces the diffusion of accelerated electrons, this spatial extent can be explained by either an enhanced magnetic field (∼80 μG) or a suppressed diffusion coefficient (∼10²⁷ cm² s⁻¹ at 100 TeV). The integrated X-ray flux, (4–6) × 10⁻¹² erg s⁻¹ cm⁻² (2–10 keV), would require a magnetic field strength higher than the Galactic mean (≳8 μG) if the diffuse X-ray emission originates from synchrotron radiation and the gamma-ray emission is predominantly hadronic. If the X-rays are of thermal origin, the measured extension, temperature, and plasma density can be explained by a jet with a luminosity of ∼2 × 10³⁹ erg s⁻¹, which is comparable to the Eddington luminosity of this system.

DOI： 10.3847/2041-8213/ad9d11

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

Abstract

Sagittarius A East is a supernova remnant with a unique surrounding environment, as it is located in the immediate vicinity of the supermassive black hole at the Galactic center, Sagittarius A$^{*}$. The X-ray emission of the remnant is suspected to show features of overionized plasma, which would require peculiar evolutionary paths. We report on the first observation of Sagittarius A East with the X-Ray Imaging and Spectroscopy Mission (XRISM). Equipped with a combination of a high-resolution microcalorimeter spectrometer and a large field-of-view CCD imager, we for the first time resolved the Fe xxv K-shell lines into fine structure lines and measured the forbidden-to-resonance intensity ratio to be $1.39 \pm 0.12$, which strongly suggests the presence of overionized plasma. We obtained a reliable constraint on the ionization temperature just before the transition into the overionization state, of $\gt\! 4\:$keV. The recombination timescale was constrained to be $\lt\! 8 \times 10^{11} \:$cm$^{-3}\:$s. The small velocity dispersion of $109 \pm 6\:$km$\:$s$^{-1}$ indicates a low Fe ion temperature $\lt\! 8\:$keV and a small expansion velocity $\lt\! 200\:$km$\:$s$^{-1}$. The high initial ionization temperature and small recombination timescale suggest that either rapid cooling of the plasma via adiabatic expansion from dense circumstellar material or intense photoionization by Sagittarius A$^{*}$ in the past may have triggered the overionization.

DOI： 10.1093/pasj/psae111

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

The X-ray binary system Cygnus X-3 (4U 2030+40, V1521 Cyg) is luminous but enigmatic owing to the high intervening absorption. High-resolution X-ray spectroscopy uniquely probes the dynamics of the photoionized gas in the system. In this Letter, we report on an observation of Cyg X-3 with the XRISM/Resolve spectrometer, which provides unprecedented spectral resolution and sensitivity in the 2–10 keV band. We detect multiple kinematic and ionization components in absorption and emission whose superposition leads to complex line profiles, including strong P Cygni profiles on resonance lines. The prominent Fe xxv Heα and Fe xxvi Lyα emission complexes are clearly resolved into their characteristic fine-structure transitions. Self-consistent photoionization modeling allows us to disentangle the absorption and emission components and measure the Doppler velocity of these components as a function of binary orbital phase. We find a significantly higher velocity amplitude for the emission lines than for the absorption lines. The absorption lines generally appear blueshifted by ∼−500–600 km s⁻¹. We show that the wind decomposes naturally into a relatively smooth and large-scale component, perhaps associated with the background wind itself, plus a turbulent, denser structure located close to the compact object in its orbit.

DOI： 10.3847/2041-8213/ad8ed0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

Abstract

We present an initial analysis of the X-Ray Imaging and Spectroscopy Mission (XRISM) first-light observation of the supernova remnant (SNR) N 132D in the Large Magellanic Cloud. The Resolve microcalorimeter has obtained the first high-resolution spectrum in the 1.6–10 keV band, which contains K-shell emission lines of Si, S, Ar, Ca, and Fe. We find that the Si and S lines are relatively narrow, with a broadening represented by a Gaussian-like velocity dispersion of $\sigma _v \sim 450$ km s$^{-1}$. However, the Fe He$\alpha$ lines are substantially broadened with $\sigma _v \sim 1670$ km s$^{-1}$. This broadening can be explained by a combination of the thermal Doppler effect due to the high ion temperature and the kinematic Doppler effect due to the SNR expansion. Assuming that the Fe He$\alpha$ emission originates predominantly from the supernova ejecta, we estimate the reverse shock velocity at the time when the bulk of the Fe ejecta were shock heated to be $-1000 \lesssim V_{\rm rs}$ (km s$^{-1}$) $\lesssim 3300$ (in the observer frame). We also find that Fe Ly$\alpha$ emission is redshifted with a bulk velocity of $\sim 890$ km s$^{-1}$, substantially larger than the radial velocity of the local interstellar medium surrounding N 132D. These results demonstrate that high-resolution X-ray spectroscopy is capable of providing constraints on the evolutionary stage, geometry, and velocity distribution of SNRs.

DOI： 10.1093/pasj/psae080

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

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We present an analysis of the first two XRISM/Resolve spectra of the well-known Seyfert-1.5 active galactic nucleus (AGN) in NGC 4151, obtained in 2023 December. Our work focuses on the nature of the narrow Fe K_α emission line at 6.4 keV, the strongest and most common X-ray line observed in AGN. The total line is found to consist of three components. Even the narrowest component of the line is resolved with evident Fe K_α,1 (6.404 keV) and K_α,2 (6.391 keV) contributions in a 2:1 flux ratio, fully consistent with neutral gas with negligible bulk velocity. Subject to the limitations of our models, the narrowest and intermediate-width components are consistent with emission from optically thin gas, suggesting that they arise in a disk atmosphere and/or wind. Modeling the three line components in terms of Keplerian broadening, they are readily associated with (1) the inner wall of the “torus,” (2) the innermost optical “broad-line region” (or “X-ray BLR”), and (3) a region with a radius of r ≃ 100 GM/c ² that may signal a warp in the accretion disk. Viable alternative explanations of the broadest component include a fast-wind component and/or scattering; however, we find evidence of variability in the narrow Fe K_α line complex on timescales consistent with small radii. The best-fit models are statistically superior to simple Voigt functions, but when fit with Voigt profiles the time-averaged lines are consistent with a projected velocity broadening of FWHM . Overall, the resolution and sensitivity of XRISM show that the narrow Fe K line in AGN is an effective probe of all key parts of the accretion flow, as it is currently understood. We discuss the implications of these findings for our understanding of AGN accretion, future studies with XRISM, and X-ray-based black hole mass measurements.

DOI： 10.3847/2041-8213/ad7397

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.3018908

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.3019329

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.3019325

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DOI： 10.1117/12.3018366

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.3016594

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Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.3019651

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.3019733

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

Abstract

The X-ray spectral state transitions of Galactic black hole transients (GBHTs) are often linked to the changes in the mass accretion rate. A narrow distribution of transition luminosity in terms of the Eddington ratio has been found in previous studies of GBHTs based on RXTE data (Maccarone, 2003, A&A, 409, 697; Vahdat Motlagh et al., 2019, MNRAS, 485, 2744) and this Eddington ratio at the transition is often used in recent studies with instruments such as Swift/XRT and NICER/XTI, covering soft energies below 1 to 10 keV. However, the X-ray states characterized by spectral parameters may have different definitions depending on the energy ranges adopted in the spectral analysis, leaving the question of whether the distribution of transition luminosity obtained with RXTE remains the same when we use the instruments covering softer energy bands. In this work, we investigated the X-ray state evolutions and the variations of luminosities of eight outbursts of seven GBHTs. We found that the bolometric luminosity of the power-law component was tightly constrained to $\sim\! 1.3\%$ Eddington luminosity at index transition when the photon index starts to decrease towards the hard state, which is consistent with the previous RXTE results (Vahdat Motlagh et al. 2019, MNRAS, 485, 2744; Kalemci et al. 2013, ApJ, 779, 95). Moreover, the tightest clustering was found to be the power-law luminosity right after the start of disk recession, with a mean logarithmic Eddington ratio of −1.84 ± 0.28. In addition, our results suggest that the disk recession starts after the bolometric disk luminosity drops below 1% Eddington luminosity.

DOI： 10.1093/pasj/psad057

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

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We present Monitor of All-sky X-ray Image (MAXI) and Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the Be X-ray binary, MAXI J0655−013, in outburst. NuSTAR observed the source once early in the outburst, when spectral analysis yields a bolometric (0.1–100 keV), unabsorbed source luminosity of L_bol = 5.6 × 10³⁶ erg s⁻¹, and a second time 54 days later, by which time the luminosity had dropped to L_bol = 4 × 10³⁴ erg s⁻¹ after first undergoing a dramatic increase. Timing analysis of the NuSTAR data reveals a neutron star spin period of 1129.09 ± 0.04 s during the first observation, which decreased to 1085 ± 1 s by the time of the second observation, indicating spin-up due to accretion throughout the outburst. Furthermore, during the first NuSTAR observation, we observed quasi-periodic oscillations (QPOs) with centroid frequency ν₀ = 89 ± 1 mHz, which exhibited a second harmonic feature. By combining the MAXI and NuSTAR data with pulse period measurements reported by Fermi/GBM, we are able to show that apparent flaring behavior in the MAXI light curve is an artifact introduced by uneven sampling of the pulse profile, which has a large pulsed fraction. Finally, we estimate the magnetic field strength at the neutron star surface via three independent methods, invoking a tentative cyclotron resonance scattering feature at 44 keV, QPO production at the inner edge of the accretion disk, and spin-up via interaction of the neutron star magnetic field with accreting material. Each of these result in a significantly different value. We discuss the strengths and weaknesses of each method and infer that MAXI J0655−013 is likely to have a high surface magnetic field strength, B_s > 10¹³ G.

DOI： 10.3847/1538-4357/ace696

DOI： 10.48550/arXiv.2306.16489

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2628772

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2629316

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

Abstract

We report the results of quasi-simultaneous multiwavelength (near-infrared, optical, UV, and X-ray) observations of the Galactic X-ray black hole binary MAXI J1820+070 performed in 2019 May 10–13, ∼60 d after the onset of the first rebrightening phase. It showed a much larger optical-to-X-ray luminosity ratio (∼8) than in the initial outburst epoch. The primary components of the spectral energy distribution (SED) can be best interpreted by a radiatively inefficient accretion flow (RIAF) spectrum showing a luminosity peak in the optical band. By comparison with theoretical calculations, we estimate the mass accretion rate to be $\dot{M}/(8 L_{\rm Edd}/c^2) \sim 10^{-3}$, where c is the light speed and LEdd is the Eddington luminosity. In addition to the RIAF emission, a blue power-law component is detected in the optical–UV SED, which is most likely synchrotron radiation from the jet. The optical spectrum taken at the Seimei telescope shows a weak and narrow Hα emission line, the emitting region of which is constrained to be ≳2 × 104 times the gravitational radius. We suggest that the entire disk structure cannot be described by a single RIAF solution but cooler material responsible for the Hα emission must exist at the outermost region.

DOI： 10.1093/pasj/psac038

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

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We report on the evolution of X-ray spectral and timing properties of the X-ray binary MAXI J1727−203 based on NICER/XTI and MAXI/GSC observations. Over the course of the outburst, a transition from the intermediate state to the high/soft state, and then back to the low/hard state was observed. During the high/soft state, the innermost radius estimated from the multi-colour disk model remained constant at $\sim 145.0\ (\frac{D}{10\ \mathrm{kpc } }) \ {(\frac{\cos i}{\cos 0^{\circ } })}^{-1/2}$ km, where D is the source distance and i is the inclination. Assuming that the binary system contain a Schwarzschild black hole and has an inclination angle of 0○ − 84○, and considering the typical Eddington ratio at the transition back to the low/hard state, the black hole mass was estimated to be M ≥ 11.5 M⊙ for a distance of D ≥ 5.9 kpc. We also attempted to constrain the black hole mass and distance with a different method by combining the results from optical and near-infrared photometric observations. We modelled the near-infrared to X-ray spectral energy distributions obtained in the outburst period with an irradiated disk model, and estimated the lower limit of the black hole mass for a given distance, assuming both accretion disk and companion star fill their Roche lobe. The lower limit was, however, found to be much higher than the constraint obtained from the X-ray data. We discuss several possible causes of this inconsistency. It is difficult to fully resolve the conflict by a single cause and hence a combination of causes is required.

DOI： 10.1093/mnras/stac1503

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

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We report the results from the broadband X-ray monitoring of the new Galactic black hole candidate MAXI J1803−298 with MAXI/GSC and Swift/BAT during its outburst. After the discovery on 2021 May 1, the soft X-ray flux below 10 keV rapidly increased for ∼10 days, then gradually decreased over five months. In the brightest phase, the source exhibited the state transition from the low/hard state to the high/soft state via the intermediate state. The broadband X-ray spectrum during the outburst is well described with a disk blackbody plus its thermal or nonthermal Comptonization. Before the transition, the source spectrum is described by a thermal Comptonization component with a photon index of ∼1.7 and an electron temperature of ∼30 keV, while a strong disk blackbody component is observed after the transition. The spectral properties in these periods are consistent with the low/hard state and the high/soft state, respectively. A sudden flux drop with a duration of a few days, unassociated with a significant change in the hardness ratio, was found in the intermediate state. A possible cause of this variation is that the mass accretion rate rapidly increased at the disk transition, which induced a strong Compton-thick outflow and scattered out the X-ray flux. Assuming a nonspinning black hole, we estimate the black hole mass of MAXI J1803−298 to be$5.8\pm 0.4\,{(\cos i/\cos 70^\circ )}^{-1/2}(D/8\,\mathrm{kpc})\,{M}_{\odot }$ (where i and D are the inclination angle and the distance, respectively) from the inner disk radius obtained in the high/soft state.

DOI： 10.3847/1538-4357/ac517b

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

We present the results of Monitor of All-sky X-ray Image (MAXI) monitoring and two Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the recently discovered faint X-ray transient MAXI J1848015. Analysis of the MAXI light curve shows that the source underwent a rapid flux increase beginning on 2020 December 20, followed by a rapid decrease in flux after only ∼5 days. NuSTAR observations reveal that the source transitioned from a bright soft state with unabsorbed, bolometric (0.1–100 keV) flux F = 6.9 ± 0.1 × 10⁻¹⁰ erg cm⁻² s⁻¹, to a low hard state with flux F = 2.85 ± 0.04 × 10⁻¹⁰ erg cm⁻² s⁻¹. Given a distance of 3.3 kpc, inferred via association of the source with the GLIMPSE-C01 cluster, these fluxes correspond to an Eddington fraction of the order of 10⁻³ for an accreting neutron star (NS) of mass M = 1.4M_⊙, or even lower for a more massive accretor. However, the source spectra exhibit strong relativistic reflection features, indicating the presence of an accretion disk that extends close to the accretor, for which we measure a high spin, a = 0.967 ± 0.013. In addition to a change in flux and spectral shape, we find evidence for other changes between the soft and hard states, including moderate disk truncation with the inner disk radius increasing from R_in ≈ 3 R_g to R_in ≈ 8 R_g, narrow Fe emission whose centroid decreases from 6.8 ± 0.1 keV to 6.3 ± 0.1 keV, and an increase in low-frequency (10⁻³–10⁻¹ Hz) variability. Due to the high spin, we conclude that the source is likely to be a black hole rather than an NS, and we discuss physical interpretations of the low apparent luminosity as well as the narrow Fe emission.

DOI： 10.3847/1538-4357/ac5258

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Language：English   Publishing type：Research paper (scientific journal)  

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

<title>Abstract</title>
SS Cyg has long been recognized as the prototype of a group of dwarf novae that show only outbursts. However, this object has entered a quite anomalous event in 2021, which at first appeared to be standstill, i.e., an almost constant luminosity state observed in Z Cam-type dwarf novae. This unexpected event gives us a great opportunity to reconsider the nature of standstill in cataclysmic variables. We have observed this anomalous event and its forerunner, a gradual and simultaneous increase in the optical and X-ray flux during quiescence, through many optical telescopes and the X-ray telescopes NICER and NuSTAR. We have not found any amplification of the orbital hump during quiescence before the anomalous event, which suggests that the mass transfer rate did not significantly fluctuate on average. The estimated X-ray flux was not enough to explain the increment of the optical flux during quiescence via X-ray irradiation of the disk and the secondary star. It would be natural to consider that viscosity in the quiescent disk was enhanced before the anomalous event, which increased mass accretion rates in the disk and raised not only the optical flux but also the X-ray flux. We suggest that enhanced viscosity also triggered the standstill-like phenomenon in SS Cyg, which is considered to be a series of small outbursts. The inner part of the disk would always stay in the outburst state and only its outer part would be unstable against the thermal–viscous instability during this phenomenon, which is consistent with the observed optical color variations. This scenario is in line with our X-ray spectral analyses which imply that the X-ray-emitting inner accretion flow became hotter than usual and vertically expanded, and that it became denser and was cooled down after the onset of the standstill-like state.

DOI： 10.1093/pasj/psab073

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE-Intl Soc Optical Eng  

DOI： 10.1117/1.jatis.7.3.037001

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4357/abe6a1

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Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4357/abde38

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/2041-8213/abaaaa

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Other Link： https://iopscience.iop.org/article/10.3847/2041-8213/abaaaa

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DOI： 10.3847/1538-4357/ab46b3

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Language：English   Publishing type：Research paper (scientific journal)  

© 2019 The Author(s). Published by Oxford University Press on behalf of the Astronomical Society of Japan. We report results from X-ray and optical observations of the Galactic black hole candidate MAXI J1828-249 performed with Suzaku and the Kanata telescope around the X-ray flux peak in the 2013 outburst. The time-averaged X-ray spectrum covering 0.6-168 keV was approximately characterized by a strong multi-color disk blackbody component with an inner disk temperature of ∼0.6 keV, and a power-law tail with a photon index of ∼2.0. We detected an additional structure at 5-10 keV, which can be modeled neither with X-ray reflection on the disk nor relativistic broadening of the disk emission. Instead, it was successfully reproduced with a Comptonization of disk photons by thermal electrons with a relatively low temperature (10 keV). We infer that the source was in the intermediate state, considering its long-term trend in the hardness intensity diagram, the strength of the spectral power-law tail, and its variability properties. The lowerature Comptonization component could be produced in a boundary region between the truncated standard disk and the hot inner flow, or a Comptonizing region that somehow developed above the disk surface. The multi-wavelength spectral energy distribution suggests that the optical and ultraviolet fluxes were dominated by irradiated outer disk emission.

DOI： 10.1093/pasj/psz091

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DOI： 10.3847/2041-8213/ab3ebf

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© 2019. The American Astronomical Society. All rights reserved.. We report results from the X-ray and optical monitoring of the black hole candidate MAXI J1820+070 (=ASSASN-18ey) over the entire period of its outburst from 2018 March to October. In this outburst, the source exhibited two sets of "fast rise and slow decay"-type long-term flux variations. We found that the 1-100 keV luminosities at two peaks were almost the same, although a significant spectral softening was only seen in the second flux rise. This confirms that the state transition from the low/hard state to the high/soft state is not determined by the mass accretion rate alone. The X-ray spectrum was reproduced with the disk blackbody emission and its Comptonization, and the long-term spectral variations seen in this outburst were consistent with a disk truncation model. The Comptonization component, with a photon index of 1.5-1.9 and electron temperature of 40 keV, was dominant during the low/hard state periods, and its contribution rapidly decreased (increased) during the spectral softening (hardening). During the high/soft-state period, in which the X-ray spectrum became dominated by the disk blackbody component, the inner disk radius was almost constant, suggesting that the standard disk was present down to the innermost stable circular orbit. The long-term evolution of optical and X-ray luminosities and their correlation suggest that the jets substantially contributed to the optical emission in the low/hard state, while they are quenched and the outer disk emission dominated the optical flux in the intermediate state and the high/soft state.

DOI： 10.3847/1538-4357/ab09ff

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DOI： 10.3847/1538-4357/aaf233

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DOI： 10.3847/1538-4357/aaea5e

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© 2018. The American Astronomical Society. All rights reserved.. We report X-ray, optical, and near-infrared monitoring of the new X-ray transient MAXI J1820+070 discovered with MAXI on 2018 March 11. Its X-ray intensity reached ∼2 crab at 2-20 keV at the end of March, and then gradually decreased until the middle of June. In this period, the X-ray spectrum was described by Comptonization of the disk emission, with a photon index of ∼1.5 and an electron temperature of ∼50 keV, which is consistent with a black hole X-ray binary in the low/hard state. The electron temperature was slightly decreased, and the photon index increased, with increasing flux. The source showed significant X-ray flux variation on a timescale of seconds. This short-term variation was found to be associated with changes in the spectral shape, and the photon index became slightly harder at higher fluxes. This suggests that the variation was produced by a change in the properties of the hot electron cloud responsible for the strong Comptonization. Modeling a multi-wavelength spectral energy distribution around the X-ray flux peak at the end of March, covering the near-infrared to X-ray bands, we found that the optical and near-infrared fluxes were likely contributed substantially by the jet emission. Before this outburst, the source was never detected in the X-ray band with MAXI (with a 3σ upper limit of ∼0.2 mcrab at 4-10 keV, obtained from seven years of data from 2009 to 2016), whereas weak optical and infrared activity was found at flux levels ∼3 orders of magnitude lower than the peak fluxes in the outburst.

DOI： 10.3847/1538-4357/aae929

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© The Author(s) 2018. Published by Oxford University Press on behalf of the Astronomical Society of Japan. All rights reserved. We report on the detection and subsequent X-ray monitoring of the new Galactic black hole candidate MAXI J1535−571 with the Gas Slit Camera onboard Monitor of All-sky X-ray Image (MAXI/GSC). After the discovery on 2017 September 2, made independently with MAXI and the Swift/BAT, the source brightened gradually, and in a few weeks reached the peak intensity of ∼5 Crab, or ∼1.6 × 10−7 erg cm−2 s−1 in terms of the 2-20 keV flux. On the initial outburst rise, the 2-20 keV MAXI/GSC spectrum was described by a power-law model with a photon index of 2, while after a hard-to-soft transition, which occurred on September 18, the spectrum required a disk blackbody component in addition. At around the flux peak, the 2-8 keV and 15-50 keV light curves showed quasi-periodic and anti-correlated fluctuations with amplitudes of 10%-20%, on a time scale of ∼1 d. Based on these X-ray properties obtained with the MAXI/GSC, with additional information from the Swift/BAT, we discuss the evolution of the spectral state of this source, and give constraints on its system parameters.

DOI： 10.1093/pasj/psy093

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© 2018. The American Astronomical Society. All rights reserved.. We present the third MAXI/GSC catalog in the high Galactic latitude sky () based on the 7-year data from 2009 August 13 to 2016 July 31, complementary to that in the low Galactic latitude sky (|b| > 10°) (Hori et al. 2018). We compile 682 sources detected at significances of s D,4-10 keV ≥ 6.5 in the 4-10 keV band. A two-dimensional image fit based on the Poisson likelihood algorithm (C-statistics) is adopted for the detections and constraints on their fluxes and positions. The 4-10 keV sensitivity reaches ≈0.48 mCrab, or ≈5.9 × 10-12 erg cm-2 s-1, over half of the survey area. Compared with the 37-month Hiroi et al. (2013) catalog, which adopted a threshold of s D,4-10 keV ≥ 7, the source number increases by a factor of ∼1.4. The fluxes in the 3-4 keV and 10-20 keV bands are further estimated, and hardness ratios (HRs) are calculated using the 3-4 keV, 4-10 keV, 3-10 keV, and 10-20 keV band fluxes. We also make the 4-10 keV light curves in 1-year bins for all the sources and characterize their variabilities with an index based on a likelihood function and the excess variance. Possible counterparts are found from five major X-ray survey catalogs by Swift, Uhuru, RXTE, XMM-Newton, and ROSAT, as well as an X-ray galaxy cluster catalog (MCXC). Our catalog provides the fluxes, positions, detection significances, HRs, 1-year bin light curves, variability indices, and counterpart candidates.

DOI： 10.3847/1538-4365/aad1ef

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DOI： 10.1093/pasj/psy118

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DOI： 10.1093/pasj/psy058

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DOI： 10.1117/12.2309455

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DOI： 10.1093/pasj/psy027

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DOI： 10.1093/pasj/psx072

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DOI： 10.1093/pasj/psx154

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DOI： 10.1093/pasj/psx138

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DOI： 10.1093/pasj/psx127

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DOI： 10.1093/pasj/psx147

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DOI： 10.1093/pasj/psy004

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DOI： 10.1093/pasj/psx156

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© 2018. The American Astronomical Society. All rights reserved.. We present the first MAXI/GSC X-ray source catalog in the low-Galactic-latitude sky outside the Galactic center region (, l < 30°, and l > 330°) based on 7-year data from 2009 August 13 to 2016 July 31. To overcome source confusion in crowded regions, we have accurately calibrated the position-dependent shape of the point-spread function of the MAXI/GSC by analyzing onboard data. We have also taken into account the Galactic ridge X-ray emission. Using a maximum likelihood image fitting method, we have detected 221 sources with a significance threshold >6.5σ, 7 of which are transients only detected in 73-day time-sliced images. The faintest source has a flux of 5.2 10-12 erg cm-2 s-1 (or an intensity of 0.43 mCrab) in the 4-10 keV band. We have identified the counterparts for about 81% of the detected sources, by cross-matching with the Swift, Uhuru, RXTE, XMM-Newton, MCXC, and ROSAT all-sky survey catalogs. Our catalog contains the source name, position and its error, flux and detection significance in the 3-4 keV, 4-10 keV, and 10-20 keV bands, hardness ratios, and information on the likely counterpart for the individual detected sources. We have obtained 73-day bin light curves of all the cataloged sources over 7 years and have calculated their periodograms. On the basis of the mean properties of time variability and spectral hardness, we suggest that the majority of the unidentified sources are low-mass X-ray binaries or blazars. Finally, we present the log N-log S relations at different Galactic longitudes and for different source populations.

DOI： 10.3847/1538-4365/aaa89c

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DOI： 10.1093/pasj/psx151

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© 2017. The American Astronomical Society. All rights reserved. We report on the detection and follow-up multi-wavelength observations of the new X-ray transient MAXI J1807+132 with the MAXI/GSC, Swift, and ground-based optical telescopes. The source was first recognized with the MAXI/GSC on 2017 March 13. About a week later, it reached maximum intensity (∼10 mCrab in 2-10 keV), and then gradually faded in ∼10 days by more than one order of magnitude. Time-averaged Swift/X-ray Telescope spectra in the decaying phase can be described by a blackbody with a relatively low temperature (0.1-0.5 keV), plus a hard power-law component with a photon index of ∼2. These spectral properties are similar to those of neutron star low-mass X-ray binaries (LMXBs) in their dim periods. The blackbody temperature and the radius of the emission region varied in a complex manner as the source became dimmer. The source was detected in the optical wavelength on March 27-31 as well. The optical flux decreased monotonically as the X-ray flux decayed. The correlation between the X-ray and optical fluxes is found to be consistent with those of known neutron star LMXBs, supporting the idea that the source is likely to be a transient neutron star LMXB.

DOI： 10.3847/1538-4357/aa93f0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

The metal abundance of the hot plasma that permeates galaxy clusters represents the accumulation of heavy elements produced by billions of supernovae(1). Therefore, X-ray spectroscopy of the intracluster medium provides an opportunity to investigate the nature of supernova explosions integrated over cosmic time. In particular, the abundance of the iron-peak elements (chromium, manganese, iron and nickel) is key to understanding how the progenitors of typical type Ia supernovae evolve and explode(2-6). Recent X-ray studies of the intracluster medium found that the abundance ratios of these elements differ substantially from those seen in the Sun(7-11), suggesting differences between the nature of type Ia supernovae in the clusters and in the Milky Way. However, because the K-shell transition lines of chromium and manganese are weak and those of iron and nickel are very close in photon energy, highresolution spectroscopy is required for an accurate determination of the abundances of these elements. Here we report observations of the Perseus cluster, with statistically significant detections of the resonance emission from chromium, manganese and nickel. Our measurements, combined with the latest atomic models, reveal that these elements have near-solar abundance ratios with respect to iron, in contrast to previous claims. Comparison between our results and modern nucleosynthesis calculations(12-14) disfavours the hypothesis that type Ia supernova progenitors are exclusively white dwarfs with masses well below the Chandrasekhar limit (about 1.4 times the mass of the Sun). The observed abundance pattern of the iron-peak elements can be explained by taking into account a combination of near-and sub-Chandrasekhar-mass type Ia supernova systems, adding to the mounting evidence that both progenitor types make a substantial contribution to cosmic chemical enrichment(5,15,16).

DOI： 10.1038/nature24301

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present optical multicolour photometry of V404 Cyg during the outburst from 2015 December to 2016 January together with the simultaneous X-ray data. This outburst occurred less than sixmonths after the previous outburst in 2015 June-July. These two outbursts in 2015 were of a slow-rise and rapid-decay type and showed large-amplitude (similar to 2mag) and short-term (similar to 10 min-3 h) optical variations even at low luminosity (0.01-0.1L(Edd)). We found correlated optical and X-ray variations in two similar to 1 h time intervals and obtained a Bayesian estimate of an X-ray delay against the optical emission, which is similar to 30-50 s, during those two intervals. In addition, the relationship between the optical and X-ray luminosities was L-opt alpha L-X(0.25-0.29) at that time. These features cannot be easily explained by the conventional picture of transient black hole binaries, such as canonical disc reprocessing and synchrotron emission related to a jet. We suggest that the disc was truncated during those intervals and that the X-ray delays represent the required time for the propagation of mass accretion flow to the inner optically thin region with a speed comparable to the free-fall velocity.

DOI： 10.1093/mnras/stx1555

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We test the proposed three-component spectral model for neutron star low-mass X-ray binaries using broad-band X-ray data. We have analysed four X-ray spectra (0.8-30 keV) obtained with Suzaku during the 2010 outburst of 4U 1608-52, which have allowed us to perform a comprehensive spectral study covering all the classical spectral states. We use a thermally Comptonized continuum component to account for the hard emission, as well as two thermal components to constrain the accretion disc and neutron star surface contributions. We find that the proposed combination of multicolour disc, single-temperature blackbody and Comptonization components successfully reproduces the data from soft to hard states. In the soft state, our study supports the neutron star surface (or boundary layer) as the dominant source for the Comptonization seed photons yielding the observed weak hard emission, while in the hard state both solutions, either the disc or the neutron star surface, are equally favoured. The obtained spectral parameters as well as the spectral/timing correlations are comparable to those observed in accreting black holes, which support the idea that black hole and neutron star low-mass X-ray binaries undergo a similar state evolution during their accretion episodes.

DOI： 10.1093/mnras/stx020

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report on an X-ray observing campaign of the ultraluminous X-ray source IC 342 X-1 with NuSTAR and Swift in 2016 October, in which we captured the very moment when the source showed spectral variation. The Swift/XRT spectrum obtained in October 9-11 has a power-law shape and is consistent with those observed in the coordinated XMM-Newton and NuSTAR observations in 2012. In October 16-17, when the 3-10 keV flux became approximate to 4 times higher, we performed simultaneous NuSTAR and Swift observations. In this epoch, the source showed a more round-shaped spectrum like that seen with ASCA23 years ago. Thanks to the wide energy coverage and high sensitivity of NuSTAR, we obtained hard X-ray data covering up to similar to 30 keV for the first time during the high-luminosity state of IC 342 X-1. The observed spectrum has a broader profile than the multi-color disk blackbody model. The X-ray flux decreased again in the last several hours of the NuSTAR observation, when the spectral shape approached those seen in 2012 and 2016 October 9-11. The spectra obtained in our observations and in 2012 can be commonly described with disk emission and its Comptonization in cool (Te approximate to 4 keV), optically thick (tau approximate to 5) plasma. The spectral turnover seen at around 5-10 keV shifts to higher energies as the X-ray luminosity decreases. This behavior is consistent with that predicted from recent numerical simulations of super-Eddington accretion flows with Compton-thick outflows. We suggest that the spectral evolution observed in IC 342 X-1 can be explained by a smooth change in mass-accretion rate.

DOI： 10.3847/1538-4357/aa67e7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

X-ray spectroscopy with Hitomi was expected to resolve the origin of the faint unidentified E approximate to 3.5 keV emission line reported in several low-resolution studies of various massive systems, such as galaxies and clusters, including the Perseus cluster. We have analyzed the Hitomi first-light observation of the Perseus cluster. The emission line expected for Perseus based on the XMM-Newton signal from the large cluster sample under the dark matter decay scenario is too faint to be detectable in the Hitomi data. However, the previously reported 3.5 keV flux from Perseus was anomalously high compared to the sample-based prediction. We find no unidentified line at the reported high flux level. Taking into account the XMM measurement uncertainties for this region, the inconsistency with Hitomi is at a 99% significance for a broad dark matter line and at 99.7% for a narrow line from the gas. We do not find anomalously high fluxes of the nearby faint K line or the Ar satellite line that were proposed as explanations for the earlier 3.5 keV detections. We do find a hint of a broad excess near the energies of high-n transitions of S XVI (E similar or equal to 3.44 keV rest-frame)-a possible signature of charge exchange in the molecular nebula and another proposed explanation for the unidentified line. While its energy is consistent with XMM pn detections, it is unlikely to explain the MOS signal. A confirmation of this interesting feature has to wait for a more sensitive observation with a future calorimeter experiment.

DOI： 10.3847/2041-8213/aa61fa

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© 2016 The Author. Published by Oxford University Press on behalf of the Astronomical Society of Japan. All rights reserved. Twenty-three giant flares from thirteen active stars (eight RS CVn systems, one Algol system, three dMe stars, and one young stellar object) were detected during the first two years of our all-sky X-ray monitoring with the gas propotional counters (GSC) of the Monitor of All-sky X-ray Image (MAXI). The observed parameters of all these MAXI/GSC flares are found to be at the upper ends for stellar flares with the luminosity of 1031-34 erg s-1 in the 2-20 keV band, the emission measure of 1054-57 cm-3, the e-folding time of 1 hr to 1.5 d, and the total radiative energy released during the flare of 1034-39 erg. Notably, the peak X-ray luminosity of 5+4-2 × 1033erg s-1 in the 2-20 keV band was detected in one of the flares on II Peg, which is one of the, or potentially the, largest-ever-observed in stellar flares. X-ray flares were detected from GT Mus, V841 Cen, SZ Psc, and TWA-7 for the first time in this survey. Whereas most of our detected sources are multiple-star systems, two of them are single stars (YZ CMi and TWA-7). Among the stellar sources within 100 pc distance, the MAXI/GSC sources have larger rotation velocities than the other sources. This suggests that the rapid rotation velocity may play a key role in generating large flares. Combining the X-ray flare data of nearby stars and the sun, taken from literature and our own data, we discovered a universal correlation of τ LX0.2 for the flare duration τ and the intrinsic X-ray luminosity LX in the 0.1-100 keV band, which holds for 5 and 12 orders of magnitude in τ and LX, respectively. The MAXI/GSC sample is located at the highest ends of the correlation.

DOI： 10.1093/pasj/psw081

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We derive the first hard X-ray luminosity function (XLF) of stellar tidal disruption events (TDEs) by supermassive black holes (SMBHs), which gives an occurrence rate of TDEs per unit volume as a function of peak luminosity and redshift, utilizing an unbiased sample observed by the Monitor of All-sky X-ray Image (MAXI). On the basis of the light curves characterized by a power-law decay with an index of -5/3, a systematic search using the MAXI data detected four TDEs in the first 37 months of observations, all of which have been found in the literature. To formulate the TDE XLF, we consider the mass function of SMBHs, that of disrupted stars, the specific TDE rate as a function of SMBH mass, and the fraction of TDEs with relativistic jets. We perform an unbinned maximum likelihood fit to the MAXI TDE list and check the consistency with the observed TDE rate in the ROSAT all-sky survey. The results suggest that the intrinsic fraction of the jet-accompanying events is 0.0007%-34%. We confirm that at z less than or similar to 1.5 the contamination of the hard X-ray luminosity functions of active galactic nuclei by TDEs is not significant and hence that their contribution to the growth of SMBHs is negligible at the redshifts.

DOI： 10.1093/pasj/psw056

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Clusters of galaxies are the most massive gravitationally bound objects in the Universe and are still forming. They are thus important probes(1) of cosmological parameters and many astrophysical processes. However, knowledge of the dynamics of the pervasive hot gas, the mass of which is much larger than the combined mass of all the stars in the cluster, is lacking. Such knowledge would enable insights into the injection of mechanical energy by the central supermassive black hole and the use of hydrostatic equilibrium for determining cluster masses. X-rays from the core of the Perseus cluster are emitted by the 50-million-kelvin diffuse hot plasma filling its gravitational potential well. The active galactic nucleus of the central galaxy NGC 1275 is pumping jetted energy into the surrounding intracluster medium, creating buoyant bubbles filled with relativistic plasma. These bubbles probably induce motions in the intracluster medium and heat the inner gas, preventing runaway radiative cooling-a process known as active galactic nucleus feedback(2-6). Here we report X-ray observations of the core of the Perseus cluster, which reveal a remarkably quiescent atmosphere in which the gas has a line-of-sight velocity dispersion of 164 +/- 10 kilometres per second in the region 30-60 kiloparsecs from the central nucleus. A gradient in the line-of-sight velocity of 150 +/- 70 kilometres per second is found across the 60-kiloparsec image of the cluster core. Turbulent pressure support in the gas is four per cent of the thermodynamic pressure, with large-scale shear at most doubling this estimate. We infer that a total cluster mass determined from hydrostatic equilibrium in a central region would require little correction for turbulent pressure.

DOI： 10.1038/nature18627

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© 2016 The Author. Published by Oxford University Press on behalf of the Astronomical Society of Japan. Various transient phenomena on a timescale ranging from seconds to days appear at unexpected sky positions in X-rays. MAXI, Monitor of All-sky X-ray Image, on the International Space Station has been monitoring about 95% of the sky a day and has detected transient objects since 2009 August. Here, we describe quasi-real-time data processing systems of MAXI and a subsequent nova-alert system to find transient objects, and present the capabilities for the nova-alert system to detect transient events with excess fluxes from ≥80 mCrab in a single scan transit to ≥8 mCrab for 4 d, and to send prompt alert information to the world in less than 30 s after the onboard detection of a burst, making the best use of the International Space Station (ISS) real-time network. We also report on highlights of scientific results obtained with the system until the end of the first extended mission phase, 2015 March. Including 15 X-ray novae solely or independently discovered, we have reported on 177 transient phenomena, such as X-ray bursts, outbursts, and state transitions of X-ray binaries and X-ray flares from active stars and blazars, via the Astronomer's Telegram, and on 63 burst phenomena of other types via the Gamma-ray Coordinates Network. We summarize the results of these transient sources and phenomena focusing on the detections with the nova-alert system, and some new transients yet unpublished or requiring attention.

DOI： 10.1093/pasj/psw016

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We revisited the unusual wind in GRO J1655-40, detected with Chandra in 2005 April, using long-term Rossi X-ray Timing Explorer X-ray data and simultaneous optical/near-infrared photometric data. This wind is the most convincing case for magnetic driving in black hole binaries, as it has an inferred launch radius that is a factor of 10 smaller than the thermal wind prediction. However, the optical and near-infrared (OIR) fluxes monotonically increase around the Chandra observation, whereas the X-ray flux monotonically decreases from 10 days beforehand. Yet the optical and near-infrared fluxes are from the outer, irradiated disk, so for them to increase implies that the X-rays likewise increased. We applied a new irradiated disk model to the multi-wavelength spectral energy distributions. Fitting the OIR fluxes, we estimated the intrinsic luminosity at the Chandra epoch was greater than or similar to 0.7L(Edd), which is more than one order of magnitude larger than the observed X-ray luminosity. These results could be explained if a Compton-thick, almost completely ionized gas was present in the wind and strong scattering reduced the apparent X-ray luminosity. The effects of scattering in the wind should then be taken into account for discussion of the wind-driving mechanism. Radiation pressure and Compton heating may also contribute to powering the wind at this high luminosity.

DOI： 10.3847/0004-637X/823/2/159

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We performed time-lag analysis on the X-ray light curves of Centaurus A (Cen A) obtained by the Gas Slit Camera (GSC) aboard the Monitor of All-sky X-ray Image (MAXI) in three energy bands (2-4 keV, 4-10 keV, and 10-20 keV). We discovered a soft X-ray lag relative to higher energies (soft lag) on a timescale of days in a flaring episode by employing the discrete correlation function (DCF) and the z-transformed discrete correlation function (ZDCF) method. In the episode, a peak and a centroid in the DCF and the ZDCF was observed at a soft lag of similar to 5 d in 2-4 keV versus 4-10 keV and in 4-10 keV versus 10-20 keV, and similar to 10 d in 2-4 keV versus 10-20 keV. We found it difficult to explain the observed X-ray variation by a single energy injection with the one-zone synchrotron self-Compton (SSC) model, in which the soft lags in these three energy bands reflect the different cooling times of the relativistic electrons, by assuming the magnetic field and minimum Lorentz factor estimated from a broad-band spectral energy distribution. Alternatively, if the phenomenon is interpreted as cooling of Comptonizing electrons in a corona covering the accretion disk, the temperature of the corona producing the variable X-rays should be similar to 10 keV for reconciliation with the soft lag in the energy range of 2-20 keV.

DOI： 10.1093/pasj/psw001

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© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. We present the results from our Suzaku observations of the Galactic black hole binary 4U 1630-47. 4U 1630-47 was observed in the very high state (VHS) during the 2012 September-October outburst. The inner disk appears slightly truncated by comparison with a previous high/soft state (HSS) of this source, even by taking into account energetic coupling between the disk and corona. The spectra do not show the Doppler-shifted emission lines indicating baryonic jets that were seen four days previously in an XMM-Newton observation, despite the source being in a similar state. There are no significant absorption lines from highly ionized iron ions. We also observed 4U 1630-47 in the HSS simultaneously with Suzaku and NuSTAR in an early epoch of the 2015 outburst. All Suzaku spectra in the HSS show variable iron-K absorption line features. We find that the ionization state of the disk wind rapidly increased when the continuum showed significant spectral hardening. This behavior is consistent with that expected from a thermally driven wind.

DOI： 10.1002/asna.201612331

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We investigate optical, infrared, and radio active galactic nucleus (AGN) signs in the merger remnant Arp 187, which hosts luminous jets launched in the order of 10(5) yr ago but whose present-day AGN activity is still unknown. We find AGN signs from the optical Baldwin-Phillips-Telervich diagram and infrared [O IV] 25.89 mu m line, originating from the narrow line regions of AGN. On the other hand, Spitzer/IRS show host galaxy dominated spectra, suggesting that the thermal emission from the AGN torus is considerably small or already diminished. Combining the black holemass, the upper limit of radio luminosity of the core, and the fundamental plane of the black hole enables us to estimate X-ray luminosity, which gives &lt; 10(40) erg s(-1). Those results suggest that the AGN activity of Arp 187 has already been quenched, but the narrow line region is still alive owing to the time delay of emission from the past AGN activity.

DOI： 10.1093/pasj/psv112

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© 2016 Macmillan Publishers Limited. All rights reserved. How black holes accrete surrounding matter is a fundamental yet unsolved question in astrophysics. It is generally believed that matter is absorbed into black holes via accretion disks, the state of which depends primarily on the mass-accretion rate. When this rate approaches the critical rate (the Eddington limit), thermal instability is supposed to occur in the inner disk, causing repetitive patterns of large-amplitude X-ray variability (oscillations) on timescales of minutes to hours. In fact, such oscillations have been observed only in sources with a high mass-accretion rate, such as GRS 1915+105 (refs 2, 3). These large-amplitude, relatively slow timescale, phenomena are thought to have physical origins distinct from those of X-ray or optical variations with small amplitudes and fast timescales (less than about 10 seconds) often observed in other black-hole binaries - for example, XTE J1118+480 (ref. 4) and GX 339â '4 (ref. 5). Here we report an extensive multi-colour optical photometric data set of V404 Cygni, an X-ray transient source containing a black hole of nine solar masses (and a companion star) at a distance of 2.4 kiloparsecs (ref. 8). Our data show that optical oscillations on timescales of 100 seconds to 2.5 hours can occur at mass-accretion rates more than ten times lower than previously thought. This suggests that the accretion rate is not the critical parameter for inducing inner-disk instabilities. Instead, we propose that a long orbital period is a key condition for these large-amplitude oscillations, because the outer part of the large disk in binaries with long orbital periods will have surface densities too low to maintain sustained mass accretion to the inner part of the disk. The lack of sustained accretion - not the actual rate - would then be the critical factor causing large-amplitude oscillations in long-period systems.

DOI： 10.1038/nature16452

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press  

We derive the first hard X-ray luminosity function (XLF) of stellar tidal disruption events (TDEs) by supermassive black holes (SMBHs), which gives an occurrence rate of TDEs per unit volume as a function of peak luminosity and redshift, utilizing an unbiased sample observed by the Monitor of All-sky X-ray Image (MAXI). On the basis of the light curves characterized by a power-law decay with an index of -5/3, a systematic search using the MAXI data detected four TDEs in the first 37 months of observations, all of which have been found in the literature. To formulate the TDE XLF, we consider the mass function of SMBHs, that of disrupted stars, the specific TDE rate as a function of SMBH mass, and the fraction of TDEs with relativistic jets.We perform an unbinned maximum likelihood fit to the MAXI TDE list and check the consistency with the observed TDE rate in the ROSAT all-sky survey. The results suggest that the intrinsic fraction of the jet-accompanying events is 0.0007%-34%. We confirm that at z ≲ 1.5 the contamination of the hard X-ray luminosity functions of active galactic nuclei by TDEs is not significant and hence that their contribution to the growth of SMBHs is negligible at the redshifts.

DOI： 10.1093/pasj/psw056

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Language：English   Publishing type：Research paper (international conference proceedings)  

© Copyright owned by the author(s) under the terms of the Creative Commons. We report on multi-color optical photometry in the 2015 outbursts of V404 Cygni, an X-ray transient. This system showed optical oscillations on timescales of 100 sec to 2.5 hours in these outbursts, and they were correlated with the simultaneous X-ray variations. On the basis of the ~1-min optical delays against X-rays and multi-wavelength SED analyses, the optical variability in this system was likely caused by X-ray reprocessing at the outer accretion disk. We also find that some repetitive optical oscillations can occur at mass accretion rates >10 times lower than previously thought. Although the mechanism of this kind of variations is still unclear, we suggest that the lack of sustained mass accretion, which would be induced in long-period systems, may be a key condition.

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.1.0_502

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The black hole mass and accretion rate in ultraluminous X-ray sources (ULXs) in external galaxies, whose X-ray luminosities exceed those of the brightest black holes in our Galaxy by hundreds and thousands of times(1,2), is an unsolved problem. Here we report that all ULXs ever spectroscopically observed have almost the same optical spectra, apparently of WNL type (late nitrogen Wolf-Rayet stars) or LBV (luminous blue variables) in their hot state, which are very scarce stellar objects. We show that the spectra do not originate from WNL/LBV-type donors but from very hot winds from the accretion disks with nearly normal hydrogen content, which have similar physical conditions to the stellar winds from these stars. The optical spectra are similar to that of SS 433, the only known supercritical accretor in our Galaxy(3), although the ULX spectra indicate a higher wind temperature. Our results suggest that ULXs with X-ray luminosities of similar to 10(40) erg s(-1) must constitute a homogeneous class of objects, which most likely have supercritical accretion disks.

DOI： 10.1038/NPHYS3348

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Monitor of All sky X-ray Image (MAXI) discovered a new outburst of an X-ray transient source named MAXI J1421-613. Because of the detection of three X-ray bursts from the source, it was identified as a neutron star low-mass X-ray binary. The results of data analyses of the MAXI GSC (Gas Slit Camera) and the Swift XRT (X-Ray Telescope) follow-up observations suggest that the spectral hardness remained unchanged during the first two weeks of the outburst. All the XRT spectra in the 0.5-10 keV band can be well explained by thermal Comptonization of multi-color disk blackbody emission. The photon index of the Comptonized component is approximate to 2, which is typical of low-mass X-ray binaries in the low/hard state. Since X-ray bursts have a maximum peak luminosity, it is possible to estimate the (maximum) distance from its observed peak flux. The peak flux of the second X-ray burst, which was observed by the GSC, is about 5 photons cm(-2) s(-1). By assuming a blackbody spectrum of 2.5 keV, the maximum distance to the source is estimated as 7 kpc. The position of this source is contained by the large error regions of two bright X-ray sources detected with Orbiting Solar Observatory-7 (OSO-7) in the 1970s. Besides this, no past activities at the XRT position are reported in the literature. If MAXI J1421-613 is the same source as ( one of) these, the outburst observed with MAXI may have occurred after a quiescence of 30-40 years.

DOI： 10.1093/pasj/psv003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The archetypical very-high-energy gamma-ray blazar Mrk 421 was monitored for more than three years with the Gas Slit Camera on board Monitor of All Sky X-ray Image (MAXI), and its long-term X-ray variability was investigated. The MAXI light curve in the 3-10 keV range was transformed into the periodogram in the frequency range f = 1 x 10(-8)-2 x 10(-6) Hz. The artifacts on the periodogram, resulting from data gaps in the observed light curve, were extensively simulated for variations with a power-law-like power spectrum density (PSD). By comparing the observed and simulated periodograms, the PSD index was evaluated as alpha = 1.60 +/- 0.25. This index is smaller than that obtained in the higher-frequency range (f greater than or similar to 1 x 10(-5) Hz), namely, alpha = 2.14 +/- 0.06 in the 1998 ASCA observation of the object. The MAXI data impose a lower limit on the PSD break at f(b) = 5 x 10(-6) Hz, consistent with the break of f(b) = 9.5 x 10(-6) Hz suggested from the ASCA data. The low-frequency PSD index of Mrk 421 derived with MAXI falls well within the range of typical values among nearby Seyfert galaxies (alpha = 1-2). The physical implications from these results are briefly discussed.

DOI： 10.1088/0004-637X/798/1/27

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

DOI： 10.1088/0004-637X/796/2/146

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Language：English   Publishing type：Research paper (scientific journal)  

We report the results from an X-ray and near-infrared observation of the Galactic black hole binary 4U 1630-47 in the very high state (VHS), performed with Suzaku and the Infrared Survey Facility around the peak of the 2012 September-October outburst. The X-ray spectrum is approximated by a steep power law, with photon index of 3.2, identifying the source as being in the VHS. A more detailed fit shows that the X-ray continuum is well described by a multicolor disk, together with thermal and nonthermal Comptonization. The inner disk appears slightly truncated by comparison with a previous high/soft state of this source, even taking into account energetic coupling between the disk and corona, although there are uncertainties due to the dust-scattering correction. The near-infrared fluxes are higher than the extrapolated disk model, showing that there is a contribution from irradiation in the outer disk and/or the companion star at these wavelengths. Our X-ray spectra do not show the Doppler-shifted iron emission lines indicating a baryonic jet that were seen four days previously in an XMM-Newton observation, despite the source being in a similar state. There are also no significant absorption lines from highly ionized iron lines as are seen in the previous high/soft state data. We show that the increased source luminosity is not enough on its own to make the wind so highly ionized as to be undetectable. This shows that the disk wind has changed in terms of its launch radius and/or density compared to the high/soft state. © 2014. The American Astronomical Society. All rights reserved..

DOI： 10.1088/0004-637X/790/1/20

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report on the results from Suzaku observations of the Galactic black hole X-ray binary H1743-322 in the low/hard state during its outburst in 2012 October. We appropriately take into account the effects of dust scattering to accurately analyze the X-ray spectra. The time-averaged spectra in the 1-200 keV band are dominated by a hard power-law component of a photon index of approximate to 1.6 with a high-energy cutoff at approximate to 60 keV, which is well described with the Comptonization of the disk emission by the hot corona. We estimate the inner disk radius from the multi-color disk component, and find that it is 1.3-2.3 times larger than the radius in the high/soft state. This suggests that the standard disk was not extended to the innermost stable circular orbit. A reflection component from the disk is detected with R = Omega/2 pi approximate to 0.6 (Omega is the solid angle). We also successfully estimate the stable disk component independent of the time-averaged spectral modeling by analyzing short-term spectral variability on a similar to 1 s timescale. A weak low-frequency quasi-periodic oscillation at 0.1-0.2 Hz is detected, whose frequency is found to correlate with the X-ray luminosity and photon index. This result may be explained by the evolution of the disk truncation radius.

DOI： 10.1088/0004-637X/789/2/100

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© The Author 2014. Published by Oxford University Press on behalf of the Astronomical Society of Japan. The Monitor of All-sky X-ray Image (MAXI) Gas Slit Camera (GSC) detects gamma-ray bursts (GRBs), including bursts with soft spectra, such as X-ray flashes (XRFs).MAXI/GSC is sensitive to the energy range from 2 to 30 keV. This energy range is lower than other currently operating instruments which are capable of detecting GRBs. Since the beginning of the MAXI operation on 2009 August 15, GSC observed 35 GRBs up to the middle of 2013. One third of them were also observed by other satellites. The rest of them show a trend to have soft spectra and low fluxes. Because of the contribution of those XRFs, the MAXI GRB rate is about three times higher than those expected from the BATSE log N-log P distribution. When we compare it to the observational results of the Wide-field X-ray Monitor on the High Energy Transient Explorer 2, which covers the the same energy range as that of MAXI/GSC, we find the possibility that many of the MAXI bursts are XRFs with Epeak lower than 20 keV. We discuss the source of soft GRBs observed only by MAXI. The MAXI log N-log S distribution suggests that the MAXI XRFs are distributed over a closer distance than hard GRBs. Since the distributions of the hardness of galactic stellar flares and X-ray bursts overlap with those of MAXI GRBs, we discuss the possibility of confusion of such galactic transients with the MAXI GRB samples.

DOI： 10.1093/pasj/psu063

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© The Author 2014. Published by Oxford University Press on behalf of the Astronomical Society of Japan. All rights reserved. We report on long-term monitoring of a newly discovered X-ray nova, MAXI J1910-057 (= Swift J1910.2-0546) by MAXI and Swift. The new X-ray transient was first detected on 2012 May 31 by the MAXI Gas Slit Camera (GSC) and the Swift Burst Alert Telescope (BAT) almost simultaneously. We analyzed X-ray and UV data for 270 d following the outburst onset taken by repeated MAXI scans and Swift pointing observations. The obtained X-ray light curve for the inital 90 d is roughly represented by a fast-rise and exponentialdecay profile. However, it re-brightened at ∼110 d after the onset and finally went down below both GSC and BAT detection limits after 240 d. All the X-ray energy spectra are fitted well with a model consisting of a multi-color-disk blackbody and its Comptonized hard tail. During the soft-state periods, the inner-disk radius of the best-fit model was almost constant. If the radius represents the innermost stable circular orbit of a nonspinning black hole and the soft-to-hard transitions occur at 1%-4% of the Eddington luminosity, the mass of the compact object is estimated to be > 2.9 M⊙ and the distance to be > 1.70 kpc. The inner-disk radius became larger in the hard/hard-intermediate state. This suggests that the accretion disk would be truncated. We detected an excess of the UV flux over the disk blackbody component extrapolated from the X-ray data, which can be modeled as reprocessed emission irradiated by the inner disk. We also found that the UV light curve mostly traced the X-ray curve, but a short dipping event was observed in both the UV and the X-ray bands with a 3.5 d X-ray time lag. This can be interpreted as the radial inflow of accreting matter from the outer UV region to the inner X-ray region.

DOI： 10.1093/pasj/psu060

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Language：English   Publishing type：Research paper (international conference proceedings)  

© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. We present our recent results from Suzaku and Swift Time-Of-Opportunity observations of the Galactic black hole transients MAXI J1305-704, H 1743-322, and 4U 1630-472. The wide-band high-quality data obtained in the low/hard state (the former two sources) and in the very high state (4U 1630-472) enable us to constrain the structure of the accretion flow in various X-ray luminosities. We find that all the spectra, including the 4U 1630-472 data, taken 4 days after the detection of the baryonic jet [2], contain strong Comptonised components and suggest disc truncation. In the H 1743-322 data, a low-frequency QPO is detected, whose frequency is found to correlate the X-ray luminosity and photon index. This may be explained by the evolution of the disc truncation radius. Considering these results, we discuss the inner disc structure of black hole binaries over a wide range of mass accretion rates.

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We report the results from X-ray studies of the newly discovered black hole candidate MAXI J1305-704 based on Suzaku and Swift observations in the low/hard and high/soft states, respectively. The long Suzaku observation shows two types of clear absorption dips, both of which recur on a dip interval of 9.74 ± 0.04 hr, which we identify with the orbital period. There is also partially ionized absorption in the nondip (persistent) emission in both the high/soft state and, very unusually, the low/hard state. However, this absorption (in both states) has substantially lower ionization than that seen in other high inclination systems, where the material forms a homogeneous disk wind. Here instead the absorption is most likely associated with clumpy, compact structures associated with the dipping material, which we see uniquely in this source likely because we view it at a very large inclination angle. A large inclination angle is also favored, together with a low black hole mass, to explain the high disk temperature seen in the fairly low luminosity high/soft state, as Doppler boosting enhances the disk temperature at high inclination. The disk radius inferred from these data is significantly smaller than that of the soft component seen in the low/hard state, supporting models where the disk is truncated at low luminosities. We find, however, that the lack of variability power on timescales of ∼50 s in the Suzaku low/hard state data is difficult to explain, even with a low-mass black hole. © 2013. The American Astronomical Society. All rights reserved..

DOI： 10.1088/0004-637X/779/1/26

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We report the results from X-ray studies of the newly discovered black hole candidate MAXI J1305-704 based on Suzaku and Swift observations in the low/hard and high/soft states, respectively. The long Suzaku observation shows two types of clear absorption dips, both of which recur on a dip interval of 9.74 ± 0.04 hr, which we identify with the orbital period. There is also partially ionized absorption in the nondip (persistent) emission in both the high/soft state and, very unusually, the low/hard state. However, this absorption (in both states) has substantially lower ionization than that seen in other high inclination systems, where the material forms a homogeneous disk wind. Here instead the absorption is most likely associated with clumpy, compact structures associated with the dipping material, which we see uniquely in this source likely because we view it at a very large inclination angle. A large inclination angle is also favored, together with a low black hole mass, to explain the high disk temperature seen in the fairly low luminosity high/soft state, as Doppler boosting enhances the disk temperature at high inclination. The disk radius inferred from these data is significantly smaller than that of the soft component seen in the low/hard state, supporting models where the disk is truncated at low luminosities. We find, however, that the lack of variability power on timescales of ∼50 s in the Suzaku low/hard state data is difficult to explain, even with a low-mass black hole. © 2013. The American Astronomical Society. All rights reserved..

DOI： 10.1088/0004-637X/779/1/26

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DOI： 10.1093/pasj/65.5.L10

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We present a catalog of high Galactic-latitude (|b| > 10°) X-ray sources detected in the first 37 months of data of the Monitor of All-sky X-ray Image/Gas Slit Camera (MAXI/GSC). To achieve the best sensitivity, we develop a background model of the GSC that well reproduces the data based on the detailed on-board calibration. Source detection is performed through image fits with a Poisson likelihood algorithm. The catalog contains 500 objects detected with significances of s D, 4-10 keV ≥ 7 in the 4-10 keV band. The limiting sensitivity is ≈7.5 × 10-12 erg cm-2 s-1 (≈0.6 mCrab) in the 4-10 keV band for 50% of the survey area, which is the highest ever achieved in an all-sky survey mission covering this energy band. We summarize the statistical properties of the catalog and results from cross matching with the Swift/BAT 70 month catalog, the meta-catalog of X-ray detected clusters of galaxies, and the MAXI/GSC 7 month catalog. Our catalog lists the source name (2MAXI), position and its error, detection significances and fluxes in the 4-10 keV and 3-4 keV bands, the hardness ratio, and the basic information of the likely counterpart available for 296 sources. © 2013. The American Astronomical Society. All rights reserved.

DOI： 10.1088/0067-0049/207/2/36

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We report on the spectral evolution of a new X-ray transient, MAXIJ0556-332, observed by MAXI, Swift, and RXTE. The source was discovered on 2011 January 11 (MJD = 55572) by the MAXI Gas Slit Camera allsky survey at (l , b) = (238.i9, -25.i2), relatively away from the Galactic plane. Swift/XRT follow-up observations identified it with a previously uncatalogued bright X-ray source, which led to optical identification. For more than one year since its appearance, MAXIJ0556-332 has been X-ray active, with a 2-10 keV intensity above 30 mCrab. The MAXI/GSC data revealed rapid X-ray brightening in the first five days, and a hard-to-soft transition in the meantime. For the following ×70 days, the 0.5-30 keV spectra, obtained by the Swift/XRT and the RXTE/PCA on an almost daily basis, show a gradual hardening, with large flux variability. These spectra are approximated by a cutoff power-law with a photon index of 0.4-1 and a high-energy exponential cutoff at 1.5-5 keV, throughout the initial 10 months where the spectral evolution is mainly represented by a change of the cutoff energy. To be more physical, the spectra are consistently explained by thermal emission from an accretion disk plus Comptonized emission from a boundary layer around a neutron star. This supports the source identification as being a neutron-star X-ray binary. The obtained spectral parameters agree with those of neutron-star X-ray binaries in the soft state, whose luminosity is higher than 1.8 × 1037 erg s-1. This suggests a source distance of >17 kpc. © 2013. Astronomical Society of Japan.

DOI： 10.1093/pasj/65.3.58

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We report on the first observation of an X-ray outburst of a Be/X-ray binary pulsar, LSV+44 17/RXJ0440.9+4431, and the discovery of an absorption dip structure in the pulse profile. An outburst of this source was discovered by MAXI GSC in 2010 April. It was the first detection of transient activity of LSV+44 17 since the source was identified as a Be/X-ray binary in 1997. From the data of a follow-up RXTE observation near the peak of the outburst, we found a narrow dip structure in its pulse profile, which was clearer in the lower-energy bands. The pulse-phase-averaged energy spectra in the 3-100 keV band could be fitted with a continuum model containing a power-law function with an exponential cutoff and a blackbody component, which are modified at low energy by an absorption component. A weak iron Kα emission line was also detected in the spectra. From the pulse-phase-resolved spectroscopy we found that the absorption column density at the dip phase was much higher than those in the other phases. The dip was not seen in subsequent RXTE observations at lower flux levels. These results suggest that the dip in the pulse profile originates from the eclipse of the radiation from the neutron star by the accretion column. © 2012. Astronomical Society of Japan.

DOI： 10.1093/pasj/64.4.79

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We report on an X-ray spectral analysis of the black hole candidate XTE J1752-223 in the 2009-2010 outburst, utilizing data obtained with the MAXI/Gas Slit Camera (GSC), the Swift/XRT, and Suzaku, which work comple-mentarily. As already reported by Nakahira et al. (2010, PASJ, 62, L27), MAXI monitored the source continuously throughout the entire outburst for about eight months. All of the MAXI/GSC energy spectra in the high/soft state, lasting for 2 months, are well represented by a multi-color disk plus power-law model. The innermost disk temperature changed from ∼0.7 keV to ∼0.4 keV and the disk flux decreased by an order of magnitude. Nevertheless, the innermost radius is constant at ∼41 D 3.5 (cos i) -1/2 km, where D 3.5 is the source distance in units of 3.5kpc and i the inclination. The multi-color disk parameters obtained with the MAXI/GSC are consistent with those with the Swift/XRT and Suzaku. The Suzaku data also suggest a possibility that the disk emission is slightly Comptonized, which could account for broad iron-K features reported previously. Assuming that the obtained innermost radius represents the innermost stable circular orbit for a non-rotating black hole, we estimate the mass of the black hole to be 5.51 ± 0.28 M ⊙ D 3.5 (cos -1/2 , where the correction for the stress-free inner boundary condition and color hardening factor of 1.7 are taken into account. If the inclination is less than 49°, as suggested from radio monitoring of transient jets, and the soft-to-hard transition in 2010 April occurred at 1%-4% of Eddignton luminosity, the fitting of the Suzaku spectra with a relativistic accretion-disk model derives constraints on the mass and the distance to be 3.1-55M ⊙ and 2.3-22 kpc, respectively. This confirms that the compact object in XTE J1752-223 is a black hole. © 2012. Astronomical Society of Japan.

DOI： 10.1093/pasj/64.1.13

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.67.1.1.0_133_2

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We present a large X-ray flare from a nearby weak-lined T Tauri star TWA-7 detected with the Gas Slit Camera (GSC) on the Monitor of All-sky X-ray Image (MAXI). The GSC captured X-ray flaring from TWA-7 with a flux of 3 × 10-9 erg cm-2 s-1 in 2-20 keV band during the scan transit starting at 2010-09-07 18:24:30 (UT). The estimated X-ray luminosity at the scan in the energy band is 3 × 1032 erg s-1, indicating that the event is among the largest X-ray flares from T Tauri stars. Since MAXI GSC monitors a target only during a scan transit of about a minute per 92 min orbital cycle, the luminosity at the flare peak might have been higher than that detected. At the scan transit, we observed a high X-ray-to-bolometric luminosity ratio, logLX=Lbol = -0.1+0.2-0.3; i.e., the X-ray luminosity is comparable to the bolometric luminosity. Since TWA-7 has neither an accreting disk nor a binary companion, the observed event implies that none of those are essential to generate such big flares in T Tauri stars. © 2011. Astronomical Society of Japan.

DOI： 10.1093/pasj/63.sp3.S713

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We constructed a new X-ray (2-10 keV) luminosity function of Compton-thin active galactic nuclei (AGNs) in the local universe, using the first MAXI/GSC source catalog surveyed in the 4-10 keV band. The sample consists of 37 non-blazar AGNs at z = 0.002-0.2,whose identification is highly (>97%) complete. We confirmed the trend that the fraction of absorbed AGNs with N H > 10 22 cm -2 rapidly decreases against the luminosity (L X ), from 0.73±0.10 at L X = 10 42-43.5 erg s -1 to 0.12±0.08 at L X = 10 43.5-45.5 erg s -1 . The obtained luminosity function was well-fitted with a smoothly connected double power-law model whose indices are γ 1 = 0.84 (fixed) and γ 2 = 2.0±0.2 below and above the break luminosity, L * = 10 43.3±0.4 erg s -1 , respectively. While the result of the MAXI/GSC agrees well with that of HEAO-1 at L X ≥ 10 43.5 erg s -1 , it gives a larger number density at the lower luminosity range. A comparison between our luminosity function in the 2-10 keV band and that in the 14-195 keV band obtained from the Swift/BAT survey indicates that the averaged broad-band spectra in the 2-200 keV band should depend on the luminosity, approximated by Γ ∼ 1.7 for L X ≤ 10 44 erg s -1 , while Γ ∼ 2.0 for L X ≥ 10 44 erg s -1 . This trend was confirmed by the correlation between the luminosities in the 2-10 keV and 14-195 keV bands in our sample. We argue that there is no contradiction in the luminosity functions between above and below 10 keV once this effect is taken into account. © 2011. Astronomical Society of Japan.

DOI： 10.1093/pasj/63.sp3.S937

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We report on the MAXI GSC X-ray monitoring of the Crab nebula and pulsar during the GeV gamma-ray flare for the period of 2010 September 18-24 (MJD 55457-55463), detected by AGILE and Fermi-LAT. There were no significant variations on the pulse phase averaged and pulsed fluxes during the gamma-ray flare on time scales from 0.5 to 5 days. The pulse profile also showed no significant change during this period. The upper limits on the variations of the pulse phase averaged and pulsed fluxes for the period MJD 55457.5-55462.5 in the 4-10 keV band were derived to be 1% and 19%, respectively, at the 90% confidence limit of the statistical uncertainty. The lack of variations in the pulsed component over the multi-wavelength range (radio, X-ray, hard X-ray, and gamma-ray) supports not a pulsar, but a nebular origin for the gamma-ray flare. © 2011. Astronomical Society of Japan.

DOI： 10.1093/pasj/63.sp3.S821

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The monitor of the all-sky X-ray image (MAXI) Gas Slit Camera (GSC) on the International Space Station (ISS) detected a gamma-ray burst (GRB) on 2009, September 26, GRB090926B. This GRB had extremely hard spectra in the X-ray energy range. Joint spectral fitting with the Gamma-ray Burst Monitor on the Fermi Gamma-ray Space Telescope shows that this burst had a peculiarly narrow spectral energy distribution, which can be represented by a Comptonized blackbody model. This spectrum can be interpreted as photospheric emission from a low baryon-load GRB fireball. Calculating the parameter of the fireball, we found the size of the base of the flow to be r 0 = (4.3±0.9) × 10 9 Y' -3/2 cm, the Lorentz factor of the plasma is Γ = (110±10) Y' 1/4 , where Y' is a ratio between the total fireball energy and the energy in the blackbody component of the gamma-ray emission. This r 0 is a factor of a few times larger, and the Lorentz factor of 110 is smaller by also factor of a few than other bursts that have blackbody components in the spectra. © 2011. Astronomical Society of Japan.

DOI： 10.1093/pasj/63.sp3.S1035

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We present the results of monitoring the galactic black hole candidate GX 3394 with the Monitor of Allsky X-ray Image (MAXI) /Gas Slit Camera in the high/soft state during an outburst in 2010. All of the spectra throughout the 8-month period were well reproduced with a model consisting of multi-color disk emission and its Comptonization component, whose fraction is ≤25% in the total flux. In spite of the flux variability over a factor of 3, the innermost disk radius is constant at Rin = 61±2 km for an inclination angle of i = 46° and a distance of d = 8 kpc. This Rin value is consistent with those of past measurementswith Tenma in the high/soft state. Assuming that the disk extends to the innermost stable circular orbit of a non-spinning black hole, we estimate the black hole mass to be M = 6.8±0.2M for i = 46° and d = 8 kpc, which is consistent with that estimated from the Suzaku observation of the previous low/hard state. Further combined with the mass function, we obtained a mass constraint of 4.3M⊙ <M < 13.3M⊙ for the allowed range of d = 6-15 kpc and i < 60°. We also discuss the spin parameter of the black hole in GX 339-4 by applying relativistic accretion disk models to the Swift/XRT data. © 2011. Astronomical Society of Japan.

DOI： 10.1093/pasj/63.sp3.S803

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We present the first unbiased source catalog of the Monitor of All-sky X-ray Image (MAXI) mission at high Galactic latitudes (|b| > 10°), produced from the first 7-month data (2009 September 1 to 2010 March 31) of the Gas Slit Camera in the 4-10 keV band. We have developed an analysis procedure to detect faint sources from the MAXI data, utilizing a maximum likelihood image fitting method, where the image response, background, and detailed observational conditions are taken into account. The catalog consists of 143 X-ray sources above the 7 σ significance level with a limiting sensitivity of ∼1.5 × 10-11 erg cm-2 s-1 (1.2mCrab) in the 4-10 keV band. Among them, we have identified 38 Galactic/LMC/SMC objects, 48 galaxy clusters, 39 Seyfert galaxies, 12 blazars, and 1 galaxy. Four other sources are confused with multiple objects, and one remains unidentified. The logN-log S relation of extragalactic objects is in good agreement with the HEAO-1 A-2 result, although the list of the brightest AGNs in the entire sky has significantly changed since that produced 30 yr ago. © 2011. Astronomical Society of Japan.

DOI： 10.1093/pasj/63.sp3.S677

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

X-ray and near-infrared (J-H-K-s) observations of the galactic black-hole binary GX 339-4 in the low/hard state were performed with Suzaku and IRSF in 2009 March. The spectrum in the 0.5-300 keV band is dominated by thermal Comptonization of multicolor disk photons, with a small contribution from a direct disk component, indicating that the inner disk is almost fully covered by hot corona with an electron temperature of approximate to 175 keV. The Comptonizing corona has at least two optical depths, tau approximate to 1, 0.4. Analysis of the iron-K line profile yields an inner-disk radius of (13.3(-6.0)(+6.04)) R-g (R-g represents the gravitational radius GM/c(2)), with the best-fit inclination angle of approximate to 50 degrees. This radius is consistent with that estimated from the continuum fit by assuming the conservation of photon numbers in Comptonization. Our results suggest that the standard disk of GX 339-4 is likely truncated before reaching the innermost stable circular orbit (for a non-rotating black hole) in the low/hard states at similar to 1% of the Eddington luminosity. The one-day averaged near-infrared light curves are found to be correlated with hard X-ray flux with F-Ks proportional to F-X(0.45). The flatter near-infrared vF(v) spectrum than the radio one suggests that the optically thin synchrotron radiation from the compact jets dominates the near-infrared flux. Based on a simple analysis, we estimate the magnetic field and size of the jet base to be 5 x 10(4) G and 6 x 10(8) cm, respectively. The synchrotron self Compton component is estimated to be approximately 0.4% of the total X-ray flux.

DOI： 10.1093/pasj/63.sp3.S785

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：CAMBRIDGE UNIV PRESS  

We report our recent results from multiwavelengths studies of microquasars, focusing on X-ray data of GX 339-4 and GRS 1915+105 obtained with Suzaku and other observatories. The broad band coverage and high energy resolution achieved with Suzaku (or a combination of Chandra/HETGS and RXTE) enable us to perform the most reliable spectral analysis both on iron-K features and continuum, and thus to best constrain the accretion disk structure of microquasars and its relation to the jet formation at various mass accretion rates.

DOI： 10.1017/S1743921310016091

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Event date： 2025.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：水戸市民会館   Country：Japan  

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Venue：水戸市民会館   Country：Japan  

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Venue：名古屋市立大学   Country：Japan  

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Venue：Nihon University   Country：Japan  

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Venue：Hotel Matsunoi Minakami   Country：Japan  

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Venue：Nihonbashi Life Science Building, Tokyo, Japan   Country：Japan  

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Event date： 2024.9

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Venue：北海道大学   Country：Japan  

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Event date： 2024.9

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Event date： 2024.9

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Venue：関西学院大学   Country：Japan  

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Event date： 2024.9

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Venue：関西学院大学   Country：Japan  

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Event date： 2024.9

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Venue：関西学院大学   Country：Japan  

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Venue：関西学院大学   Country：Japan  

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Event date： 2024.8

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Venue：千葉大学   Country：Japan  

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Event date： 2024.6

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Venue：Yokohama, Japan   Country：Japan  

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Event date： 2024.6

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Venue：Yokohama, Japan   Country：Japan  

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Venue：Yokohama, Japan   Country：Japan  

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Venue：Yokohama, Japan   Country：Japan  

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Venue：Yokohama, Japan   Country：Japan  

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Event date： 2024.6

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Venue：Yokohama, Japan   Country：Japan  

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Event date： 2024.6

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Venue：Yokohama   Country：Japan  

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Event date： 2024.5

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Venue：京都大学理学部４号館  

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Event date： 2024.5

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Venue：Parador de La Granja (Spain)  

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Event date： 2024.3

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Event date： 2024.3

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Event date： 2024.3

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Event date： 2024.3

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Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

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Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

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Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

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Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

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Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

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Event date： 2024.2

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：宇宙科学研究所 相模原キャンパス   Country：Japan  

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Event date： 2024.2

Language：Japanese   Presentation type：Oral presentation (invited, special)  

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Event date： 2023.10

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

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Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：国立天文台 三鷹キャンパス   Country：Japan  

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Event date： 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都大学   Country：Japan  

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Event date： 2023.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Sissi   Country：Greece  

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Event date： 2023.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Pelham   Country：Germany  

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Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2023.3

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2023.3

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2023.3

Language：English   Presentation type：Oral presentation (invited, special)  

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Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2023.1

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2023.1

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2023.1

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2022.10

Presentation type：Oral presentation (invited, special)  

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Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2022.9

Language：English   Presentation type：Oral presentation (general)  

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Event date： 2022.9

Presentation type：Oral presentation (general)  

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Event date： 2022.9

Presentation type：Oral presentation (general)  

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Event date： 2022.9

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Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2022.3

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Event date： 2022.3

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Event date： 2022.3

Presentation type：Oral presentation (general)  

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Event date： 2022.3

Presentation type：Oral presentation (general)  

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Event date： 2022.3

Presentation type：Oral presentation (general)  

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Event date： 2022.3

Presentation type：Oral presentation (general)  

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Event date： 2022.3

Presentation type：Oral presentation (general)  

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Event date： 2022.3

Presentation type：Oral presentation (general)  

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Event date： 2022.1

Presentation type：Poster presentation  

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Event date： 2022.1

Presentation type：Poster presentation  

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Event date： 2022.1

Presentation type：Poster presentation  

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Event date： 2022.1

Language：Japanese   Presentation type：Poster presentation  

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Event date： 2021.9

Language：English   Presentation type：Poster presentation  

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Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2021.9

Presentation type：Oral presentation (general)  

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Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2021.1 - 2021.2

Language：English   Presentation type：Oral presentation (invited, special)  

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Other Link： https://www.cospar-assembly.org/admin/session_cospar.php?session=896

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (invited, special)  

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Event date： 2020.3

Language：Japanese   Presentation type：Oral presentation (keynote)  

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Event date： 2018.11

Language：English   Presentation type：Oral presentation (general)  

Venue：ISAS, Japan  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：埼玉大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：理化学研究所  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島大学  

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Language：English  

Venue：Brindisi, Italy  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：埼玉大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：埼玉大学  

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Language：Japanese   Presentation type：Poster presentation  

Venue：宇宙科学研究所  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：国立天文台三鷹キャンパス  

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Language：Japanese   Presentation type：Poster presentation  

Venue：宇宙科学研究所  

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Language：English  

Venue：Ehime University, Japan  

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Language：English  

Venue：Ehime University, Japan  

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Language：Japanese   Presentation type：Poster presentation  

Venue：宇宙科学研究所  

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Language：English  

Venue：Ehime University, Japan  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：国際基督教大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：国際基督教大学  

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Language：English  

Venue：Ehime University, Japan  

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Language：English  

Venue：Ehime University, Japan  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：国際基督教大学  

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Language：Japanese  

Venue：国際基督教大学  

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Language：English  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：筑波大学  

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Language：English   Presentation type：Poster presentation  

Venue：Berlin, Germany  

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Language：English   Presentation type：Poster presentation  

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Language：English  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：山形大学  

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Language：English  

Venue：Taipei, Taiwan  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：広島大学  

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Language：English  

Venue：La Sapienza Univ., Roma, Italy  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宇宙科学研究所  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東海大学  

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Language：Japanese   Presentation type：Poster presentation  

Venue：甲南大学  

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Language：Japanese   Presentation type：Poster presentation  

Venue：宇宙科学研究所  

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Language：English  

Venue：ESAC, Madrid, Spain  

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Language：English  

Venue：Nara Women's University, Japan  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：首都大学東京  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北学院大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：首都大学東京  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：首都大学東京  

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Language：Japanese   Presentation type：Poster presentation  

Venue：大阪大学  

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Language：English  

Venue：ESAC, Madrid, Spain  

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Language：English   Presentation type：Oral presentation (general)  

Venue：ISAS, Japan  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学  

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Language：English  

Venue：Rome, Italy  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学  

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Language：Japanese   Presentation type：Poster presentation  

Venue：九州大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学  

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Language：Japanese   Presentation type：Poster presentation  

Venue：宇宙科学研究所  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学  

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Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：倉敷市芸文館  

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Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：京都大学  

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Language：English   Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (invited, special)  

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Language：Japanese   Presentation type：Poster presentation  

Venue：宇宙科学研究所  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉大学  

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Language：English  

Venue：Pasadena, California, USA  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉大学  

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Language：English  

Venue：RIKEN, Japan  

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Language：English  

Venue：RIKEN, Japan  

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Language：English  

Venue：RIKEN, Japan  

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Language：Japanese   Presentation type：Poster presentation  

Venue：宇宙科学研究所  

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Language：English  

Venue：RIKEN, Japan  

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Language：Japanese   Presentation type：Poster presentation  

Venue：宇宙科学研究所  

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Language：Japanese   Presentation type：Poster presentation  

Venue：愛媛大学  

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Language：Japanese   Presentation type：Poster presentation  

Venue：愛媛大学  

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Language：English  

Venue：Strasbourg, France  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：山形大学  

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Language：Japanese   Presentation type：Poster presentation  

Venue：山形大学  

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Language：Japanese   Presentation type：Poster presentation  

Venue：山形大学  

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Language：English  

Venue：RIKEN, Japan  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：埼玉大学  

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Language：Japanese   Presentation type：Poster presentation  

Venue：龍谷大学  

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Language：English   Presentation type：Poster presentation  

Venue：Atami, Japan  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：関西学院大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：国立天文台三鷹キャンパス  

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Language：English  

Venue：Mykonos island, Greece  

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Language：English  

Venue：Mykonos island, Greece  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛媛大学  

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Language：English   Presentation type：Poster presentation  

Venue：Kyoto, Japan  

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Language：Japanese   Presentation type：Poster presentation  

Venue：宇宙科学研究所  

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Language：English  

Venue：Kyoto University, Japan  

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Language：Japanese   Presentation type：Poster presentation  

Venue：大分大学  

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Language：Japanese   Presentation type：Poster presentation  

Venue：宇宙科学研究所  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉大学  

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Language：Japanese   Presentation type：Poster presentation  

Venue：宇宙科学研究所  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：兵庫県立大学  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：兵庫県立大学  

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Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Sigtuna, Sweden  

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Language：Japanese   Presentation type：Poster presentation  

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Language：Japanese   Presentation type：Poster presentation  

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Language：Japanese   Presentation type：Poster presentation  

Venue：宇宙科学研究所  

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Type：Lecture

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Audience： General

Type：Lecture

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Type：Internet

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