arXiv subjects

Hironori Matsumoto

Publications and source records attributed to Hironori Matsumoto.

At least 91 records · Page 5Linked to original sources

arXiv2008

X-Ray Reflection Nebulae with Large Equivalent Widths of Neutral Iron Ka Line in the Sgr C Region

This paper reports on the first results of the Suzaku observation in the Sgr C region. We detected four diffuse clumps with strong line emission at 6.4keV, Ka from neutral or low-ionized Fe. One of them, M359.38-0.00, is newly discovered with Suzaku. The X-ray spectra of the two bright clumps, M359.43-0.07 and M359.47-0.15, after subtracting the Galactic center diffuse X-ray emission (GCDX), exhibit strong Ka line from FeI with large equivalent widths (EWs) of 2.0-2.2keV and clear Kb of FeI. The GCDX in the Sgr C region is composed of the 6.4keV- and 6.7keV-associated components. These are phenomenologically decomposed by taking relations between EWs of the 6.4keV and 6.7keV lines. Then the former EWs against the associated continuum in the bright clump regions are estimated to be 2.4(+2.3_-0.7)keV. Since the two different approaches give similar large EWs of 2keV, we strongly suggest that the 6.4keV clumps in the Sgr C region are due to X-ray reflection/fluorescence (the X-ray reflection nebulae).

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arXiv2008

X-Ray Observation of Very High Energy Gamma-Ray Source, HESS J1745-303, with Suzaku

Suzaku observations of a TeV unidentified (unID) source, HESS J1745-303, are presented. A possible excess of neutral iron line emission is discovered, and is likely associated with the main part of HESS J1745-303, named "region A". It may be an X-ray reflection nebula where the X-rays from previous Galactic Center (GC) activity are reflected by a molecular cloud. This result further strengthens the assumption that the molecular cloud which is spatially coincident with region A of HESS J1745-303 is located in the GC region. The TeV emission from molecular clouds is reminiscent of the diffuse TeV gamma-rays from the GC giant molecular clouds, and it could have the same emission mechanism. With deep exposure mapping observations by Suzaku, a tight upper-limit on the 2-10 keV continuum diffuse emission from region A is obtained, as 2.1x10^-13ergs s^-1cm^-2. The flux ratio between 1-10 TeV and 2-10 keV is larger than 4. Possible scenarios to reproduce wide-band spectra from keV to TeV are examined. Thermal X-rays from nearby two old supernova remnants, G359.0-0.9 and G359.1-0.5, are detected, and their emission properties are well determined in the present study with deep exposure.

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arXiv2008

New CTI Correction Method for the Spaced-Row Charge Injection of the Suzaku X-Ray Imaging Spectrometer

The charge transfer inefficiency (CTI) of the X-ray CCDs on board the Suzaku satellite (X-ray Imaging Spectrometers; XIS) has increased since the launch due to radiation damage, and the energy resolution has been degraded. To improve the CTI, we have applied a spaced-row charge injection (SCI) technique to the XIS in orbit; by injecting charges into CCD rows periodically, the CTI is actively decreased. The CTI in the SCI mode depends on the distance between a signal charge and a preceding injected row, and the pulse height shows periodic positional variations. Using in-flight data of onboard calibration sources and of the strong iron line from the Perseus cluster of galaxies, we studied the variation in detail. We developed a new method to correct the variation. By applying the new method, the energy resolution (FWHM) at 5.9 keV at March 2008 is ~155 eV for the front-illuminated CCDs and ~175 eV for the back-illuminated CCD.

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arXiv2008

Iron Emission Lines on the Galactic Ridge Observed with Suzaku

In order to elucidate origin of the Galactic Ridge X-ray Emission, we analyzed Suzaku data taken at various regions along the Galactic plane and studied their Fe-K emission line features. Suzaku resolved the Fe line complex into three narrow lines at ~6.4 keV,~6.7 keV and ~6.97 keV, which are K-lines from neutral (or low-ionized), He-like, and H-like iron ions, respectively. The 6.7 keV line is clearly seen in all the observed regions and its longitudinal distribution is consistent with that determined from previous observations. The 6.4 keV emission line was also found in various Galactic plane regions (b~0). Differences in flux ratios of the 6.4 keV/6.7 keV and 6.97 keV/6.7 keV lines between the Galactic plane and the Galactic center regions are studied and its implication is discussed.

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arXiv2008

Suzaku Observations of M82 X-1 : Detection of a Curved Hard X-ray Spectrum

A report is presented on Suzaku observations of the ultra-luminous X-ray source X-1 in the starburst galaxy M82, made three time in 2005 October for an exposure of ~ 30 ks each. The XIS signals from a region of radius 3 around the nucleus defined a 2-10 keV flux of 2.1 x 10^-11 erg s-1 cm-2 attributable to point sources. The 3.2-10 keV spectrum was slightly more convex than a power-law with a photon index of 1.7. In all observations, the HXD also detected signals from M82 up to ~ 20 keV, at a 12-20 keV flux of 4.4 x 10^-12 erg s-1 cm-2 . The HXD spectrum was steeper than that of the XIS. The XIS and HXD spectra can be jointly reproduced by a cutoff power-law model, or similar curved models. Of the detected wide-band signals, 1/3 to 2/3 are attributable to X-1, while the remainder to other discrete sources in M82. Regardless of the modeling of these contaminants, the spectrum attributable to X-1 is more curved than a power-law, with a bolometric luminosity of (1.5 -3) x 10 ^40 erg s-1. These results are interpreted as Comptonized emission from a black hole of 100-200 solar masses, radiating roughly at the Eddington luminosity.

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arXiv2008

Energy-Scale Calibration of the Suzaku X-Ray Imaging Spectrometer Using the Checker Flag Charge Injection Technique in Orbit

The X-ray Imaging Spectrometer (XIS) on board the Suzaku satellite is an X-ray CCD camera system that has superior performance such as a low background, high quantum efficiency, and good energy resolution in the 0.2-12 keV band. Because of the radiation damage in orbit, however, the charge transfer inefficiency (CTI) has increased, and hence the energy scale and resolution of the XIS has been degraded since the launch of July 2005. The CCD has a charge injection structure, and the CTI of each column and the pulse-height dependence of the CTI are precisely measured by a checker flag charge injection (CFCI) technique. Our precise CTI correction improved the energy resolution from 230 eV to 190 eV at 5.9 keV in December 2006. This paper reports the CTI measurements with the CFCI experiments in orbit. Using the CFCI results, we have implemented the time-dependent energy scale and resolution to the Suzaku calibration database.

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arXiv2008

Suzaku Observation of the Ophiuchus Galaxy Cluster: One of the Hottest Cool Core Clusters

We present the analysis of a Suzaku observation of the Ophiuchus galaxy cluster. We confirmed that the cluster has a cool core. While the temperature of the intracluster medium (ICM) decreases toward the center, the metal abundance increases. Except for the core (r<~50 kpc), the cluster is hot (~9-10 keV) and is almost isothermal for r<~1 Mpc; the latter contradicts a previous study. We do not detect the variation of the redshift of the ICM in the cluster; the upper limit of the velocity difference is 3000 km s^-1. The iron line ratios in X-ray spectra indicate that the ICM has reached the ionization equilibrium state. From these results, we conclude that the Ophiuchus cluster is not a major merger cluster but one of the hottest clusters with a cool core. We obtain the upper limit of non-thermal emission from the cluster, which is consistent with both the recent claimed detection with INTEGRAL and the recent upper limits with the Swift/BAT. If the cluster has bright non-thermal emission as suggested by the INTEGRAL measurement, it is probably not due to a recent major cluster merger.

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arXiv2008

Discoveries of 3 K-shell Lines of Iron and a Coherent Pulsation of 593-sec from SAX J1748.2-2808

SAX J1748.2$-$2808 is a unique X-ray object with a flat spectrum and strong emission lines at 6.4--7.0 keV. The Suzaku satellite resolved the emission lines into 3 K-shell lines from neutral and highly ionized irons. A clear coherent pulsation with a period of 593-sec was found from the Suzaku and XMM-Newton archives. These facts favor that SAX J1748.2$-$2808 isan intermediate polar, a subclass of magnetized white dwarf binary (cataclysmic variable: CV). This paper reports on details of the findings and discusses the origin of this source.

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arXiv2008

Spatial Distribution of the Galactic Center Diffuse X-Rays and the Spectra of the Brightest 6.4keV Clumps

The high energy resolution and low background, particularly in the hard X-ray band, of the X-ray Imaging Spectrometer onboard Suzaku provide excellent spectra of the Galactic center diffuse X-rays (GCDX). This paper reports on the results of spatially resolved spectroscopy of GCDX. The most pronounced features of GCDX are the K-shell transition lines from neutral (FeI) and He-like (FeXXV) irons at energies of 6.4keV and 6.7keV, respectively. The fluxes of these lines are non-uniformly and asymmetrically distributed with respect to Sgr A*. The 6.4keV lines are particularly bright on the positive side of the Galactic longitude (east-side) with clumpy structures. A bright clump near the GC exhibits a time variability over a timescale of a few years. Neither the 6.4keV nor 6.7keV line flux shows close proportionality to the continuum flux (5--10keV band); the 6.4keV line shows excess on the high flux side, and vice versa for the 6.7keV line. On the other hand, the sum of the 6.4keV plus 6.7keV line fluxes with a ratio of 1:2 shows good proportionality to the continuum flux, and hence we phenomenologically decomposed the continuum flux of the GCDX into the 6.4keV- and 6.7keV-associated continuums with a flux ratio of 1:2. Based on these facts, we have tried to estimate the contribution of diffuse and integrated flux of point sources to the GCDX.

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arXiv2008

Time Variability of the Neutral Iron Lines from the Sgr B2 Region and its Implication of a Past Outburst of Sgr A$^*$

We investigate long-term X-ray behaviors from the Sgr B2 complex using archival data of the X-ray satellites Suzaku, XMM-Newton, Chandra and ASCA. The observed region of the Sgr B2 complex includes two prominent spots in the Fe I K-$α$ line at 6.40 keV, a giant molecular cloud M 0.66$-$0.02 known as the ``Sgr B2 cloud'' and an unusual X-ray source G 0.570$-$0.018. Although these 6.40 keV spots have spatial extensions of a few pc scale, the morphology and flux of the 6.40 keV line has been time variable for 10 years, in contrast to the constant flux of the Fe XXV-K$α$ line at 6.67 keV in the Galactic diffuse X-ray emission. This time variation is mostly due to M 0.66$-$0.02; the 6.40 keV line flux declined in 2001 and decreased to 60% in the time span 1994--2005. The other spot G 0.570$-$0.018 is found to be conspicuous only in the Chandra observation in 2000. From the long-term time variability ($\sim$10 years) of the Sgr B2 complex, we infer that the Galactic Center black hole Sgr A$^*$ was X-ray bright in the past 300 year and exhibited a time variability with a period of a few years.

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arXiv2008

High Metallicity of the X-Ray Gas up to the Virial Radius of a Binary Cluster of Galaxies: Evidence of Galactic Superwinds at High-Redshift

We present an analysis of a Suzaku observation of the link region between the galaxy clusters A399 and A401. We obtained the metallicity of the intracluster medium (ICM) up to the cluster virial radii for the first time. We determine the metallicity where the virial radii of the two clusters cross each other (~2 Mpc away from their centers) and found that it is comparable to that in their inner regions (~0.2 Zsun). It is unlikely that the uniformity of metallicity up to the virial radii is due to mixing caused by a cluster collision. Since the ram-pressure is too small to strip the interstellar medium of galaxies around the virial radius of a cluster, the fairly high metallicity that we found there indicates that the metals in the ICM are not transported from member galaxies by ram-pressure stripping. Instead, the uniformity suggests that the proto-cluster region was extensively polluted with metals by extremely powerful outflows (superwinds) from galaxies before the clusters formed. We also searched for the oxygen emission from the warm--hot intergalactic medium in that region and obtained a strict upper limit of the hydrogen density (nH<4.1x10^-5 cm^-3).

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arXiv2007

Discovery of Extended X-Ray emission from the unidentified TeV source HESS J1614-518 using the Suzaku Satellite

We report the Suzaku results of HESS J1614-518, which is the brightest extended TeV gamma-ray source discovered in the Galactic plane survey conducted using the H.E.S.S. telescope. We discovered three X-ray objects in the field of view of the X-ray Imaging Spectrometer (XIS), which were designated as Suzaku J1614-5141 (src A), Suzaku J1614-5152 (src B), and Suzaku J1614-5148 (src C). Src A is an extended source located at the peak position of HESS J1614-518, and therefore it is a plausible counterpart to HESS J1614-518. The X-ray flux in the 2-10 keV band is 5e-13 erg/s/cm^2, which is an order of magnitude smaller than the TeV flux. The photon index is 1.7, which is smaller than the canonical value of synchrotron emissions from high-energy electrons found in some supernova remnants. These findings present a challenge to models in which the origin of the TeV emission is the inverse Compton scattering of the cosmic microwave background by accelerated electrons that emit X-rays via synchrotron emission. Src B is located at a relatively dim region in the TeV band image; however, its hydrogen column density is the same as that of src A. Therefore, src B may also be physically related to HESS J1614-518. Src C is a foreground late-type B star. We also discovered a soft extended X-ray emission near HESS J1614-518.

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arXiv2007

Suzaku Spectroscopy of an X-Ray Reflection Nebula and a New Supernova Remnant Candidate in the Sgr B1 Region

We made a 100 ks observation of the Sagittarius (Sgr) B1 region at (l, b) = (0.5, -0.1) near to the Galactic center (GC) with the Suzaku/XIS. Emission lines of S XV, Fe I, Fe XXV, and Fe XXVI were clearly detected in the spectrum. We found that the Fe XXV and Fe XXVI line emissions smoothly distribute over the Sgr B1 and B2 regions connecting from the GC. This result suggests that the GC hot plasma extends at least up to the Sgr B region with a constant temperature. There are two diffuse X-ray sources in the observed region. One of the two (G0.42-0.04) is newly discovered, and exhibits a strong S XV Ka emission line, suggesting a candidate for a supernova remnant located in the GC region. The other one (M0.51-0.10), having a prominent Fe I Ka emission line and a strongly absorbed continuum, is likely to be an X-ray reflection nebula. There is no near source bright enough to irradiate M0.51-0.10. However, the Fe I Ka emission can be explained if Sgr A* was ~ 10^6 times brighter 300 years ago, the light travel time for 100 pc to M0.51-0.10, than it is at present.

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arXiv2007

Suzaku X-Ray Spectroscopy of a Peculiar Hot Star in the Galactic Center Region

We present the results of a Suzaku study of a bright point-like source in the 6.7 keV intensity map of the Galactic center region. We detected an intense FeXXV 6.7 keV line with an equivalent width of ~1 keV as well as emission lines of highly ionized Ar and Ca from a spectrum obtained by the X-ray Imaging Spectrometer. The overall spectrum is described very well by a heavily absorbed (~2x10^{23}cm^{-2}) thin thermal plasma model with a temperature of 3.8+/-0.6 keV and a luminosity of ~3x10^{34} erg s^{-1} (2.0--8.0 keV) at 8 kpc. The absorption, temperature, luminosity, and the 6.7 keV line intensity were confirmed with the archived XMM-Newton data. The source has a very red (J-Ks=8.2 mag) infrared spectral energy distribution (SED), which was fitted by a blackbody emission of ~1000 K attenuated by a visual extinction of ~31 mag. The high plasma temperature and the large X-ray luminosity are consistent with a wind-wind colliding Wolf-Rayet binary. The similarity of the SED to those of the eponymous Quintuplet cluster members suggests that the source is a WC-type source.

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arXiv2007

A Time-Variable X-Ray Echo: Indications of a Past Flare of the Galactic-Center Black Hole

A time-variability study of the neutral iron line flux at 6.40keV in the Sgr B2 region from data of Suzaku and Chandra is presented. The highly ionized iron line at 6.68keV is due to Galactic Center Diffuse X-rays (GCDX), and is thus time invariable. By comparing the 6.68keV and 6.40keV line fluxes, we found that the 6.40keV flux from the SgrB2 complex region is time variable; particularly the giant molecular cloud M0.66-0.02, known as ``Sgr B2 cloud'' is highly variable. The variability of the 6.40keV line in intensity and spatial distribution strongly supports the scenario that the molecular clouds in the SgrB2 region are X-ray Reflection Nebulae irradiated by the Galactic Center (GC) black hole Sgr A*.

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arXiv2007

Development of an n-channel CCD, CCD-NeXT1, for Soft X-ray Imager onboard the NeXT satellite

NeXT (New X-ray Telescope) is the next Japanese X-ray astronomical satellite mission after the Suzaku satellite. NeXT aims to perform wide band imaging spectroscopy. Due to the successful development of a multilayer coated mirror, called a supermirror, NeXT can focus X-rays in the energy range from 0.1 keV up to 80 keV. To cover this wide energy range, we are in the process of developing a hybrid X-ray camera, Wideband X-ray Imager (WXI) as a focal plane detector of the supermirror. The WXI consists of X-ray CCDs (SXI) and CdTe pixelized detectors (HXI), which cover the lower and higher X-ray energy bands of 0.1-80 keV, respectively. The X-ray CCDs of the SXI are stacked above the CdTe pixelized detectors of the HXI. The X-ray CCDs of the SXI detect soft X-rays below $\sim$ 10 keV and allow hard X-rays pass into the CdTe detectors of the HXI without loss. Thus, we have been developing a "back-supportless CCD" with a thick depletion layer, a thinned silicon wafer, and a back-supportless structure. In this paper, we report the development and performances of an evaluation model of CCD for the SXI, "CCD-NeXT1". We successfully fabricated two types of CCD-NeXT1, unthinned CCDs with 625-um thick wafer and 150-um thick thinned CCDs. By omitting the polishing process when making the thinned CCDs, we confirmed that the polishing process does not impact the X-ray performance. In addition, we did not find significant differences in the X-ray performance between the two types of CCDs. The energy resolution and readout noise are $\sim$ 140 eV (FWHM) at 5.9 keV and $\sim$5 electrons (RMS), respectively. The estimated thickness of the depletion layer is $\sim$80 um. The performances almost satisfy the requirements of the baseline plan of the SXI.

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arXiv2006

Suzaku Observation of Diffuse X-ray Emission from the Carina Nebula

We studied extended X-ray emission from the Carina Nebula taken with the Suzaku CCD camera XIS on 2005 Aug. 29. The X-ray morphology, plasma temperature and absorption to the plasma are consistent with the earlier Einstein results. The Suzaku spectra newly revealed emission lines from various species including oxygen, but not from nitrogen. This result restricts the N/O ratio significantly low, compared with evolved massive stellar winds, suggesting that the diffuse emission is originated in an old supernova remnant or a super shell produced by multiple supernova remnants. The X-ray spectra from the north and south of Eta Carinae showed distinct differences between 0.3-2 keV. The south spectrum shows strong L-shell lines of iron ions and K-shell lines of silicon ions, while the north spectrum shows them weak in intensity. This means that silicon and iron abundances are a factor of 2-4 higher in the south region than in the north region. The abundance variation may be produced by an SNR ejecta, or relate to the dust formation around the star forming core.

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arXiv2006

X-ray Spectral Study of the extended emission,'the Cap', located 11.6 kpc above the disk of M82

The extended X-ray emission from 'the Cap' region located 11' (11.6 kpc) above the disk of the starburst galaxy M82 has been observed with Suzaku and XMM-Newton. Owing to the good energy resolution and the large collecting area of the XIS on Suzaku, combined with similar properties of the EPIC instrument on XMM-Newton, we have clearly detected K-shell emission lines from O VII, O VIII, Ne X, Mg XI, Mg XII and the Fe-L complex. Two optically-thin thermal plasma components are required to fit the observed X-ray spectra. We have determined the metal abundances of O, Ne, Mg, Si and Fe in this region for the first time. Their metal abundance ratios agree well with those of metal-poor stars and the model prediction of metals synthesized by type-II supernovae, but they are not consistent with the metallicities of type-Ia supernovae. This result is support for the idea that the origin of the metals in the Cap is type-II supernovae explosions occurring in the starburst regions in the M82 galaxy. We discuss the possible contribution from sputtered dust grains to the metals in the Cap. An emission line consistent with the C VI transition of n=4 to 1 at 0.459 keV is marginally detected, although it is not statistically significant at the 99% confidence level; the presence of this line would suggest charge-exchange processes in the Cap.

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