arXiv subjects

Katsuji Koyama

Publications and source records attributed to Katsuji Koyama.

At least 55 records · Page 3Linked to original sources

arXiv2014

The ASTRO-H X-ray Astronomy Satellite

The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions developed by the Institute of Space and Astronautical Science (ISAS), with a planned launch in 2015. The ASTRO-H mission is equipped with a suite of sensitive instruments with the highest energy resolution ever achieved at E > 3 keV and a wide energy range spanning four decades in energy from soft X-rays to gamma-rays. The simultaneous broad band pass, coupled with the high spectral resolution of Delta E < 7 eV of the micro-calorimeter, will enable a wide variety of important science themes to be pursued. ASTRO-H is expected to provide breakthrough results in scientific areas as diverse as the large-scale structure of the Universe and its evolution, the behavior of matter in the gravitational strong field regime, the physical conditions in sites of cosmic-ray acceleration, and the distribution of dark matter in galaxy clusters at different redshifts.

astro-ph.IM↗

arXiv2014

Global Distribution of Ionizing and Recombining Plasmas in the Supernova Remnant G290.1$-$0.8

We report on the Suzaku results of the mixed-morphology supernova remnant (SNR) G290.1$-$0.8 (MSH 11-61A). The SNR has an asymmetric structure extended to the southeast and the northwest. In the X-ray spectra of the center and the northwest regions, we discover recombining plasma features with the strong Si Ly$α$ and radiative recombination continuum at $\sim$ 2.7 keV. These features are the most significant in the northwest region, and the spectra are well-reproduced with a recombining plasma of $kT_{\rm e} = 0.5$ keV. Whereas the spectra of other regions are expressed by an ionizing plasma of $kT_{\rm e} = 0.6$ keV. The recombining plasma has over-solar abundances, while the ionizing plasma has roughly solar abundances. Hence they are likely ejecta and interstellar medium (ISM) origin, respectively. The recombining plasma in the northwest of G290.1$-$0.8 would be generated by a break-out of the supernova ejecta from a high density circumstellar medium to a low density ISM.

astro-ph.HE↗

arXiv2014

Discovery of Recombining Plasma in the Supernova Remnant 3C 391

Recent X-ray study of middle-aged supernova remnants (SNRs) reveals strong radiative recombination continua (RRCs) associated with overionized plasmas, of which the origin still remains uncertain. We report our discovery of an RRC in the middle-aged SNR 3C 391. If the X-ray spectrum is fitted with a two-temperature plasma model in collisional ionization equilibrium (CIE), residuals of Si XIV Ly alpha line at 2.006 keV, S XVI Ly alpha line at 2.623 keV and the edge of RRC of Si XIII at 2.666 keV are found. The X-ray spectrum is better described by a composite model consisting of a CIE plasma and a recombining plasma (RP). The abundance pattern suggests that the RP is associated to the ejecta from a core-collapse supernova with a progenitor star of 15 solar mass. There is no significant difference of the recombining plasma parameters between the southeast region and the northwest region surrounded by dense molecular clouds. We also find a hint of Fe I K alpha line at 6.4 keV (~2.4 sigma detection) from the southeast region of the SNR.

astro-ph.HE↗

arXiv2014

X-ray Filament with a Strong 6.7 keV Line in the Galactic Center Region

An elongated X-ray source with a strong K-shell line from He-like iron (Fe XXVI) is found at (RA, Dec)_{J2000.0}=(17h44m00s.0, -29D13'40''.9) in the Galactic center region. The position coincides with the X-ray thread, G359.55+0.16, which is aligned with the radio non-thermal filament. The X-ray spectrum is well fitted with an absorbed thin thermal plasma (apec) model. The best-fit temperature, metal abundance, and column density are 4.1^{+2.7}_{-1.8} keV, 0.58^{+0.41}_{-0.32} solar, and 6.1^{+2.5}_{-1.3}x10^{22} cm^{-2}, respectively. These values are similar to those of the largely extended Galactic center X-ray emission.

astro-ph.HE↗

arXiv2014

Discovery of an Overlapping Cluster in Abell 1674 Field with Suzaku

We present the results of a Suzaku observation of Abell 1674, an optically very rich (richness class 3) cluster cataloged as z = 0.1066. We discover the He-like Fe K-shell line from the central region for the first time, and find that the X-ray spectrum yields a high redshift of 0.215^{+0.007}_{-0.006}. On the other hand, the spectrum of the southwestern region is fitted with a redshift of 0.11 \pm 0.02 by the He-like Fe L-shell lines, consistent with the optically determined value. The gas temperature, metal abundance, and core radius of the X-ray emission in the central region are 3.8 \pm 0.2 keV, 0.20 \pm 0.05 Z_solar and 450 \pm 40 kpc, respectively, while those in the southwestern region are 2.0 \pm 0.2 keV, 0.41^{+0.17}_{-0.13} Z_solar and 220^{+90}_{-70} kpc, respectively. These parameters are typical for clusters. We thus conclude that Abell 1674 consists of two independent clusters, A1674-C at z ~0.22 and A1674-SW at z ~0.11, overlapping along the line of sight. The X-ray luminosities of A1674-C within r = 2 Mpc is 15.9 \pm 0.6 \times 10^{43} erg s^{-1} in the 0.1-2.4 keV energy band, while that for A1674-SW is 1.25 \pm 0.07 \times 10^{43} erg s^{-1}. Both are consistent with those expected from the L-T relation of clusters within a factor of 2. This is another support for our conclusion.

astro-ph.HE↗

arXiv2014

Abundances in the Ejecta of Core Collapse Supernova Remnants, G350.1-0.3 and G349.7+0.2

We present Suzaku results of the two Galactic supernova remnants (SNRs), G350.1-0.3 and G349.7+0.2. We find Al and Ni K alpha lines from both the SNRs for the first time, in addition to previously detected K-shell lines of Mg, Si, S, Ar, Ca and Fe. The spectra are well described by two optically thin thermal plasmas: a low-temperature (low-kT) plasma in collisional ionization equilibrium and a high-temperature (high-kT) plasma in non-equilibrium ionization. Since the low-kT plasma has solar metal abundances, it is thought to be of interstellar medium origin. The high-kT plasma has super-solar abundances, hence it is likely to be of ejecta origin. The abundance patterns of the ejecta components are similar to those of core-collapse supernovae with the progenitor mass of ~15-25 M_solar for G350.1-0.3 and ~35-40 M_solar for G349.7+0.2. We find extremely high abundances of Ni compared to Fe (Z_Ni/Z_Fe ~8). Based on the measured column densities between the SNRs and the near sky background, we propose that G350.1-0.3 and G349.7+0.2 are located at the distance of 9+/-3 kpc and 12+/-5 kpc, respectively. Then the ejecta masses are estimated to be ~13 M_solar and ~24 M_solar for G350.1-0.3 and G349.7+0.2, respectively. These values are consistent with the progenitor mass of ~15-25 M_solar and ~35-40 M_solar for G350.1-0.3 and G349.7+0.2, respectively.

astro-ph.HE↗

arXiv2014

Discovery of Enhanced Radiative Recombination Continua of He-like Iron and Calcium from IC 443 and Its Implications

We present deep observations of the Galactic supernova remnant IC 443 with the {\it Suzaku X-ray satellite}. We find prominent K-shell lines from iron and nickel, together with a triangle residual at 8--10~keV, which corresponds to the energy of the radiative recombination continuum (RRC) of He-like iron. In addition, the wavy residuals have been seen at $\sim$5.1 and $\sim$5.5~keV. We confirm that the residuals show the first enhanced RRCs of He- and H-like calcium found in supernova remnants. These facts provide robust evidence for the recombining plasma. We reproduce the plasma in the 3.7--10~keV band using a recombining plasma model at the electron temperature 0.65~keV. The recombination parameter $n_{\rm e}t$ ($n_{\rm e}$ is electron density and $t$ is elapsed time after formation of a recombining plasma) and abundances of iron and nickel are strongly correlated, and hence the errors are large. On the other hand, the ratio of nickel to iron relative to the solar abundances is well constrained to 11$^{+4}_{-3}$ (1$σ$). A possibility is that the large abundance ratio is a result of an asymmetric explosion of the progenitor star.

astro-ph.HE↗

arXiv2014

Suzaku Discovery of Fe K-Shell Line from the O-Rich SNR G292.0+1.8

We report the Suzaku/XIS results of the Galactic oxygen-rich supernova remnant (SNR), G292.0+1.8, a remnant of a core-collapse supernova. The X-ray spectrum of G292.0+1.8 consists of two type plasmas, one is in collisional ionization equilibrium (CIE) and the other is in non-equilibrium ionization (NEI). The CIE plasma has nearly solar abundances, and hence would be originated from the circumstellar and interstellar mediums. The NEI plasma has super-solar abundances, and the abundance pattern indicates that the plasma originates from the supernova ejecta with a main sequence of 30-35 Msolar. Iron K-shell line at energy of 6.6 keV is detected for the first time in the NEI plasma.

astro-ph.HE↗

arXiv2013

X-Ray Emission from the Galactic Supernova Remnant G12.0-0.1

We present results of the Suzaku/XIS observation around the radio supernova remnant (SNR) G12.0-0.1. No significant diffuse emission extending in or along the radio shell was observed. Instead two compact X-ray sources, Suzaku J181205-1835 and Suzaku J181210-1842, were found in or near G12.0-0.1. Suzaku J181205-1835 is located at the northwest of the radio shell of G12.0-0.1. The X-ray profile is slightly extended over the point spread function of the Suzaku telescope. The X-ray spectrum has no line-like structure and is well represented by a power-law model with a photon index of 2.2 and an absorption column of N_{H}=4.9x10^{22} cm^{-2}. The distances of Suzaku J181205-1835 and G12.0-0.1 are estimated from the absorption column and the Sigma-D relation, respectively, and are nearly the same with each other. These results suggest that Suzaku J181205-1835 is a candidate of a pulsar wind nebula associated with G12.0-0.1. From its location, Suzaku J181210-1842 would be unrelated object to G12.0-0.1. The X-ray profile is point-like and the spectrum is thin thermal emission with Fe K-lines at 6.4, 6.7, and 6.97 keV, similar to those of cataclysmic variables.

astro-ph.HE↗

arXiv2013

Suzaku observations of the type 2 QSO in the central galaxy of the Phoenix cluster

We report the \Suzaku/XIS and HXD and \Chandra/ACIS-I results on the X-ray spectra of the Phoenix cluster at the redshift $z=0.596$. The spectrum of the intracluster medium (ICM) is well-reproduced with the emissions from a low temperature ($\sim3.0$\,keV and $\sim0.76$\,solar) and a high temperature ($\sim11$\,keV and $\sim0.33$\,solar) plasmas; the former is localized at the cluster core, while the latter distributes over the cluster. In addition to these ICM emissions, a strongly absorbed power-law component is found, which is due to an active galactic nucleus (AGN) in the cluster center. The absorption column density and unobscured luminosity of the AGN are $\sim3.2\times10^{23}$\,cm$^{-2}$ and $\sim4.7\times10^{45}$\,ergs\,s$^{-1}$ (2-10\,keV), respectively. Furthermore, a neutral iron (\ion{Fe}{1}) K-shell line is discovered for the first time with the equivalent width (EW) of $\sim150$\,eV at the rest frame. The column density and the EW of the \ion{Fe}{1} line are exceptionally large for such a high luminosity AGN, and hence the AGN is classified as a type 2 quasi-stellar object (QSO). We speculate that the significant fraction of the ICM cooled gas would be consumed to maintain the torus and to activate the type 2 QSO. The Phoenix cluster has a massive starburst in the central galaxy, indicating suppression in the cooling flow is less effective. This may be because the onset of the latest AGN feedback has occurred recently and it has not yet been effective. Alternatively, the AGN feedback is predominantly in radiative-mode not in kinetic-mode and the torus may work as a shield to reduce its effect.

astro-ph.CO↗

arXiv2013

Thermal and Non-thermal X-Rays from the Galactic Supernova Remnant G348.5+0.1

We report on Suzaku results of the two distinct regions in the Galactic supernova remnant G348.5+0.1: extended thermal X-rays ("soft diffuse") at the northeast region and non-thermal X-rays (CXOU J171419.8-383023) at the northwest region. The X-ray spectrum of the soft diffuse is fitted with neither an ionization equilibrium nor a non-equilibrium (ionizing) plasma model, leaving saw-teeth residuals in the 1.5-3 keV energy band. The residual structures can be produced when free electrons are recombined to the K-shells of highly ionized Mg and Si ions. In fact, the X-ray spectrum is nicely fitted with a recombination-dominant plasma model. We propose a scenario that the plasma in nearly full ionized state at high temperature quickly changed to a recombining phase due to selective cooling of electrons to a lower temperature of ~0.5 keV. The spectrum of CXOU J171419.8-383023 is well explained by a simple power-law model with a photon index of 1.9, nearly equal to the typical value of pulsar wind nebulae. Since the distance is estimated to be the same as that of the soft diffuse, we infer that both the soft diffuse and CXOU J171419.8-383023 are associated with the same object, SNR G348.5+0.1.

astro-ph.HE↗

arXiv2013

X-Ray Observation of the Galactic Supernova Remnant G355.6-0.0 with Suzaku

We present results of the Galactic supernova remnant (SNR) G355.6-0.0 observed with Suzaku. We resolved the diffuse emission detected with ASCA into two objects, G355.6-0.0 and a point-like source, Suzaku J173530-3236. The X-ray emission from G355.6-0.0 exhibits a center-filled morphology within the radio shell. The X-ray spectrum is well represented by a thin thermal plasma model with enhanced metal abundances. The spatial and spectral properties imply that G355.6-0.0 is a member of the mixed-morphology SNRs. The NH value of ~ 6 x 10^{22} cm^{-2} supports that G355.6-0.0 is a distant SNR. Suzaku J173530-3236 exhibits a hard X-ray spectrum with a strong Fe emission line, similar to those of cataclysmic variables. The NH value of ~ 3 x 10^{22} cm^{-2} is smaller than that of G355.6-0.0, and hence Suzaku J173530-3236 is located at the near side of G355.6-0.0.

astro-ph.HE↗

arXiv2013

Asymmetric Ejecta Distribution in SN 1006

We present the results from deep X-ray observations (~400 ks in total) of SN 1006 by the X-ray astronomy satellite Suzaku. The thermal spectrum from the entire supernova remnant (SNR) exhibits prominent emission lines of O, Ne, Mg, Si, S, Ar, Ca, and Fe. The observed abundance pattern in the ejecta components is in good agreement with that predicted by a standard model of Type Ia supernovae (SNe). The spatially resolved analysis reveals that the distribution of the O-burning and incomplete Si-burning products (Si, S, and Ar) is asymmetric, while that of the C-burning products (O, Ne, and Mg) is relatively uniform in the SNR interior. The peak position of the former is clearly shifted by 5' (~3.2 pc at a distance of 2.2 kpc) to the southeast from the SNR's geometric center. Using the SNR age of ~1000 yr, we constrain the velocity asymmetry (in projection) of ejecta to be ~3100 km/s. The abundance of Fe is also significantly higher in the southeast region than in the northwest region. Given that the non-uniformity is observed only among the heavier elements (Si through Fe), we argue that SN 1006 originates from an asymmetric explosion, as is expected from recent multi-dimensional simulations of Type Ia SNe, although we cannot eliminate the possibility that an inhomogeneous ambient medium induced the apparent non-uniformity. Possible evidence for the Cr K-shell line and line broadening in the Fe K-shell emission is also found.

astro-ph.HE↗

arXiv2013

Non-Thermal Radio and Gamma-Ray Emission from a Supernova Remnant by the Blast Wave Breaking Out of the Circumstellar Matter

We calculate synchrotron radio emission and gamma-ray emission due to bremsstrahlung, inverse-Compton scattering and $pi^0$-decay from the remnant of supernova which exploded in the circumstellar matter (CSM) formed by the progenitor's stellar wind. This sort of situation is a possible origin of mixed-morphology supernova remnants (SNRs) like W49B, which exhibit recombination-radiation spectra in X-ray emission. We assume that the CSM of 1.5 $M_{odot}$ exists at 0.07--3 pc away from the supernova in the interstellar medium (ISM) of density 0.016 cm$^{-3}$. When the blast wave breaks out of the CSM into the ISM, its velocity rapidly increases and hence particle acceleration is enhanced. The maximum energy of protons reaches $sim$ 1300 TeV just after the break-out with $sim$ 0.5% of the explosion energy. We consider the non-thermal emission from the blast-shocked ISM shell after the break-out. Synchrotron radio flux at 1 GHz is tens Jy, comparable to the observed from mixed-morphology SNRs. Because of low density, the gamma-ray luminosity is dominated by inverse-Compton scattering, which is higher than the $pi^0$-decay luminosity by an order of magnitude. The total gamma-ray luminosity including bremsstrahlung is of the order of $10^{33}$ erg s$^{-1}$ lower than the typical value $10^{35}$--$10^{36}$ erg s$^{-1}$ observed from mixed-morphology SNRs. However, if, e.g., $sim$10% of accelerated protons interact with some matter of density $sim$100 cm$^{-3}$, $pi^0$-decay gamma-ray luminosity would be enhanced to be comparable with the observed value.

astro-ph.HE↗

arXiv2013

Dynamics of X-Ray-Emitting Ejecta in the Oxygen-Rich Supernova Remnant Puppis A Revealed by the XMM-Newton RGS

Using the unprecedented spectral resolution of the reflection grating spectrometer (RGS) onboard XMM-Newton, we reveal dynamics of X-ray--emitting ejecta in the oxygen-rich supernova remnant Puppis A. The RGS spectrum shows prominent K-shell lines, including O VII He_alpha forbidden and resonance, O VIII Ly_alpha, O VIII Ly_beta, and Ne IX He_alpha resonance, from an ejecta knot positionally coincident with an optical oxygen-rich filament (the so-called Omega filament in the northeast of the remnant). We find that the line centroids are blueshifted by 1480+/-140+/-60 km/s (the first and second term errors are measurement and calibration uncertainties, respectively), which is fully consistent with that of the optical Omega filament. Line broadening at 654 eV (corresponding to O VIII Ly_alpha) is obtained to be less than ~0.9 eV, indicating an oxygen temperature of less than ~30 keV. Analysis of XMM-Newton MOS spectra shows an electron temperature of ~0.8 keV and an ionization timescale of ~2e10 cm^-3 s. We show that the oxygen and electron temperatures as well as the ionization timescale can be reconciled if the ejecta knot was heated by a collisionless shock whose velocity is ~600-1200 km/s and was subsequently equilibrated due to Coulomb interactions. The RGS spectrum also shows relatively weak K-shell lines of another ejecta feature located near the northeastern edge of the remnant, from which we measure redward Doppler velocities of 650+/-70+/-60 km/s.

astro-ph.HE↗

arXiv2012

X-ray Echo from the Sagittarius C Complex and 500-year Activity History of Sagittarius A*

This paper presents the Suzaku results obtained for the Sagittarius (Sgr) C region using the concept of X-ray reflection nebulae (XRNe) as the echo of past flares from the super massive black hole, Sgr A*. The Sgr C complex is composed of several molecular clouds proximately located in projected distance. The X-ray spectra of Sgr C were analyzed on the basis of a view that XRNe are located inside the Galactic center plasma X-ray emission with an oval distribution around Sgr A*. We found that the XRNe are largely separated in the line-of-sight position, and are associated with molecular clouds in different velocity ranges detected by radio observations. We also applied the same analysis to the Sgr B XRNe and completed a long-term light curve for Sgr A* occurring in the past. As a new finding, we determined that Sgr A* was experiencing periods of high luminosity already 500 years ago, which is longer than the previously reported value. Our results are consistent with a scenario that Sgr A* was continuously active with sporadic flux variabilities of Lx = 1-3 x 10^39 erg s^-1 in the past 50 to 500 years. The average past luminosity was approximately 4-6 orders of magnitude higher than that presently observed. In addition, two short-term flares of 5-10 years are found. Thus, the past X-ray flare should not be a single short-term flare, but can be interpreted as multiple flares superposed on a long-term high state.

astro-ph.GA↗

arXiv2012

The ASTRO-H X-ray Observatory

The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the high-energy universe via a suite of four instruments, covering a very wide energy range, from 0.3 keV to 600 keV. These instruments include a high-resolution, high-throughput spectrometer sensitive over 0.3-2 keV with high spectral resolution of Delta E < 7 eV, enabled by a micro-calorimeter array located in the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers covering 5-80 keV, located in the focal plane of multilayer-coated, focusing hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12 keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the 40-600 keV band. The simultaneous broad bandpass, coupled with high spectral resolution, will enable the pursuit of a wide variety of important science themes.

astro-ph.IM↗

arXiv2012

The K-shell Line Distribution of Heavy Elements along the Galactic Plane Observed with Suzaku

We report the global distribution of the intensities of the K-shell lines from the He-like and H-like ions of S, Ar, Ca and Fe along the Galactic plane. From the profiles, we clearly separate the Galactic center X-ray emission (GCXE) and the Galactic ridge X-ray emission (GRXE). The intensity profiles of the He-like K$α$ lines of S, Ar, Ca and Fe along the Galactic plane are approximately similar with each other, while not for the H-like Ly$α$ lines. In particular, the profiles of H-like Ly$α$ of S and Fe show remarkable contrast; a large excess of Fe and almost no excess of S lines in the GCXE compared to the GRXE. Although the prominent K-shell lines are represented by $\sim$1 keV and $\sim$7 keV temperature plasmas, these two temperatures are not equal between the GCXE and GRXE. In fact, the spectral analysis of the GCXE and GRXE revealed that the $\sim$1 keV plasma in the GCXE has lower temperature than that in the GRXE, and vice versa for the $\sim$7 keV plasma.

astro-ph.HE↗