arXiv subjects

Manabu Ishida

Publications and source records attributed to Manabu Ishida.

At least 73 records · Page 4Linked to original sources

arXiv2013

Progenitor Type Identification for Supernova Remnant N103B in the Large Magellanic Cloud by Suzaku and Chandra Observations

This paper presents a detailed analysis of supernova remnant (SNR) N103B located in the Large Magellanic Cloud (LMC), based on Suzaku and Chandra observations. The spectrum of the entire SNR was reproduced using 3 ISM components with the kT of 0.32, 0.56, and 0.92keV and one ejecta component of 3.96keV, based on spectral analysis of the Suzaku/XIS data. The ejecta was overabundant in heavy elements, such as Mg, Si, S, Ca, Fe, and Ni. The unprecedentedly high quality of data obtained by XIS, allowed us to correctly distinguish between the emissions from the ISM and the ejecta for the first time. Combining XIS spectral analysis with Chandra/ACIS image analysis, we verified that the ejecta distributions for elements from Si to Fe-K were similar to one another, although Fe-K emission was located slightly inward compared with that of lighter elements such as Si, S, Ar, and Ca. The onion-like structure of the ejecta was maintained after the SN. In addition, the ISM emission represented by O and Fe-L was located inside the ejecta emission. We compared hydrogen-rich ejecta plasma, which is indicative of Type II SNRs, with plasma rich in heavy elements and poor in hydrogen, which is mainly observed in Type Ia. In the case of N103B, we could not determine whether the origin of the continuum emission in the 4.0-6.0keV band was from ejecta or high-temperature ISM only based on the spectral modeling of XIS data. High-energy continuum images in the 5.2-6.0keV band obtained by ACIS were extremely similar to those of ejecta, implying that the origin of the high-energy continuum might indeed be the ejecta. By combining spectral analysis with high-energy continuum images, we found some indications for H-dominated plasma, and as a result, that the progenitor of N103B might have been a Type II. The progenitor mass was estimated to be 13 Msun based on the abundance patterns of Mg, Fe, and Ni relative to Si.

astro-ph.HE↗

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

Suzaku X-Ray Observation of the Dwarf Nova Z Camelopardalis at the Onset of an Optical Outburst

We present the result of a Suzaku X-ray spectroscopic observation of the dwarf nova Z Camelopardalis, which was conducted by chance at the onset of an optical outburst. We used the X-ray Imaging Spectrometer (a 38 ks exposure) and the Hard X-ray Detector (34 ks) to obtain a 0.35-40 keV spectrum simultaneously. Spectral characteristics suggest that the source was in the X-ray quiescent state despite being in the rising phase of an outburst in the optical band. The spectrum shows a clear signature of circumstellar absorption in excess of interstellar absorption and the reprocessed emission features of Fe fluorescence and Compton scattering. The extra absorption is explained due to partial coverage by either neutral or ionized matter. We found a spectral change during the observation, which is attributable only to the change in the circumstellar absorption. Such an X-ray spectral variation is reported for the first time in dwarf novae. We speculate that the variation in the circumstellar absorption is interpreted as a time-varying disk wind or geometrically flaring disk around the white dwarf during the propagation of a heat wave inward along the accretion disk at the beginning of the outburst, in which optical outburst and X-ray quiescent states co-exist.

astro-ph.HE↗

arXiv2011

Evolution of Synchrotron X-rays in Supernova Remnants

A systematic study of the synchrotron X-ray emission from supernova remnants (SNRs) has been conducted. We selected a total of 12 SNRs whose synchrotron X-ray spectral parameters are available in the literature with reasonable accuracy, and studied how their luminosities change as a function of radius. It is found that the synchrotron X-ray luminosity tends to drop especially when the SNRs become larger than ~5 pc, despite large scatter. This may be explained by the change of spectral shape caused by the decrease of the synchrotron roll-off energy. A simple evolutionary model of the X-ray luminosity is proposed and is found to reproduce the observed data approximately, with reasonable model parameters. According to the model, the total energy of accelerated electrons is estimated to be 10^(47-48) ergs, which is well below the supernova explosion energy. The maximum energies of accelerated electrons and protons are also discussed.

astro-ph.HE↗

arXiv2011

Suzaku Observation of the Intermediate Polar V1223 Sagittarii

We report on the Suzaku observation of the intermediate polar V1223 Sagittarii. Using a multi-temperature plasma emission model with its reflection from a cold matter, we obtained the shock temperature to be 37.9^{+5.1}_{-4.6} keV. This constrains the mass and the radius of the white dwarf (WD) in the ranges 0.82^{+0.05}_{-0.06} solar masses and (6.9+/-0.4)x10^8 cm, respectively, with the aid of a WD mass-radius relation. The solid angle of the reflector viewed from the post-shock plasma was measured to be Omega/2pi = 0.91+/-0.26. A fluorescent iron Kalpha emission line is detected, whose central energy is discovered to be modulated with the WD rotation for the first time in magnetic-CVs. Detailed spectral analysis indicates that the line comprises of a stable 6.4 keV component and a red-shifted component, the latter of which appears only around the rotational intensity-minimum phase. The equivalent width (EW) of the former stable component ~80 eV together with the measured Omega indicates the major reflector is the WD surface, and the shock height is not more than 7% of the WD radius. Comparing this limitation to the height predicted by the Aizu model (1973), we estimated the fractional area onto which the accretion occurs to be < 7x10^{-3}$ of the WD radius, which is the most severe constraint in non-eclipsing IPs. The red-shifted iron line component, on the other hand, can be interpreted as emanating from the pre-shock accretion flow via fluorescence. Its EW (28^{+44}_{-13} eV) and the central energy (6.30_{-0.05}^{+0.07} keV) at the intensity-minimum phase are consistent with this interpretation.

astro-ph.GA↗

arXiv2011

Near-Infrared and X-Ray Observations of XSS J12270-4859

XSS J12270-4859 (J12270) is an enigmatic source of unknown nature. Previous studies revealed that the source has unusual X-ray temporal characteristics, including repetitive short-term flares followed by spectral hardening, non-periodic dips, and dichotomy in activity; i.e. intervals filled with flares and those without. Together with a power-law X-ray spectrum, it is suggested to be a low-mass X-ray binary (LMXB). In order to better understand the object, we present the results of our near-infrared (NIR) photometry and linear polarimetry observations as well as X-ray spectroscopy observations, which overlap with each other partially in time, taken respectively with the InfraRed Survey Facility (IRSF) and the Rossi X-ray Timing Explorer (RXTE). We detected several simultaneous NIR and X-ray flares for the first time. No significant NIR polarization was obtained. We assembled data taken with IRSF, RXTE, Suzaku, Swift, and other missions in the literature and compared the flare profile and the spectral energy distribution (SED) with some representative high-energy sources. Based on some similarities of the repetitive NIR and X-ray flaring characteristics and the broad SED, we argue that J12270 is reminiscent of microquasars with a synchrotron jet, which is at a very low luminosity state of ~1e-4 Eddington luminosity for a stellar mass black hole or neutron star at a reference distance of 1 kpc.

astro-ph.HE↗

arXiv2010

The ASTRO-H Mission

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 by performing high-resolution, high-throughput spectroscopy with moderate angular resolution. ASTRO-H covers very wide energy range from 0.3 keV to 600 keV. ASTRO-H allows a combination of wide band X-ray spectroscopy (5-80 keV) provided by multilayer coating, focusing hard X-ray mirrors and hard X-ray imaging detectors, and high energy-resolution soft X-ray spectroscopy (0.3-12 keV) provided by thin-foil X-ray optics and a micro-calorimeter array. The mission will also carry an X-ray CCD camera as a focal plane detector for a soft X-ray telescope (0.4-12 keV) and a non-focusing soft gamma-ray detector (40-600 keV) . The micro-calorimeter system is developed by an international collaboration led by ISAS/JAXA and NASA. The simultaneous broad bandpass, coupled with high spectral resolution of Delta E ~7 eV provided by the micro-calorimeter will enable a wide variety of important science themes to be pursued.

astro-ph.IM↗

arXiv2010

Cross-calibration of the X-ray Instruments onboard the Chandra, INTEGRAL, RXTE, Suzaku, Swift, and XMM-Newton Observatories using G21.5-0.9

Context. The Crab nebula has been used as a celestial calibration source of the X-ray flux and spectral shape for many years by X-ray astronomy missions. However, the object is often too bright for current and future missions equipped with instruments with improved sensitivity. Aims. We use G21.5-0.9 as a viable, fainter substitute to the Crab, which is another pulsar-wind nebula with a time-constant powerlaw spectrum with a flux of a few milli Crab in the X-ray band. Using this source, we conduct a cross-calibration study of the instruments onboard currently active observatories: Chandra ACIS, Suzaku XIS, Swift XRT, XMM-Newton EPIC (MOS and pn) for the soft-band, and INTEGRAL IBIS-ISGRI, RXTE PCA, and Suzaku HXD-PIN for the hard band. Methods. We extract spectra from all the instruments and fit them under the same astrophysical assumptions. We compare the spectral parameters of the G21.5-0.9 model: power-law photon index, H-equivalent column density of the interstellar photoelectric absorption, flux in the soft (2-8 keV) or hard (15-50 keV) energy band. Results. We identify the systematic differences in the best-fit parameter values unattributable to the statistical scatter of the data alone. We interpret these differences as due to residual cross-calibration problems. The differences can be as large as 20% and 9% for the soft-band flux and power-law index, respectively, and 46% for the hard-band flux. The results are plotted and tabulated as a useful reference for future calibration and scientific studies using multiple missions.

astro-ph.HE↗

arXiv2010

Identification of CXOU J171405.7-381031 as a New Magnetar with XMM-Newton

We have observed the 3.8 s pulsar CXOU J171405.7-381031 with XMM-Newton, and discovered the significant dP/dt of 6.40+/-0.14X10^-11 s/s from this source for the first time, with the aid of archival Chandra data. The characteristic age (950 yr), the magnetic field strength (5X10^14 G), and the spin-down luminosity (4.5X10^34 erg/s) derived from P and dP/dt lead us to conclude that CXOU J171405.7-381031 should be identified as a new magnetar. The obtained characteristic age indicates that CXOU J171405.7-381031 is youngest among all known anomalous X-ray pulsars, which is consistent with the age estimation from the thermal X-rays of the associated supernova remnant. The ratio between 2-10 keV luminosity and spin-down luminosity is almost unity, which implies that CXOU J171405.7-381031 is the key source to connect magnetars and traditional radio pulsars.

astro-ph.HE↗

arXiv2010

Suzaku Observations of the Supernova Remnant N23 in the Large Magellanic Cloud

X-ray emission from the supernova remnant N23 in the Large Magellanic Cloud (LMC) is studied using the X-ray Imaging Spectrometer (XIS) onboard Suzaku. Thanks to superior energy resolution of the XIS in the soft X-ray band, we resolved H-like and He-like Oxygen Kαemission lines from N23 with unprecedentedly high quality, and as a result, identified a new optically thin thermal emission component with a temperature ~0.2 keV, as well as that with a temperature of ~0.5-0.7 keV previously known. This alters the estimate of the ionization timescale net from ~10^{10-11} cm^-3s to >~10^{12} cm^{-3}s. Under the assumption that N23 is still in the Sedov phase, its age evaluated from the newly discovered low temperature component is ~8000 yr, although it is possible that N23 has already moved into the radiative phase. The abundances of the heavy elements are found to be roughly consistent with those of the LMC average, which indicates that the origin of the X-ray emission of N23 is swept-up ambient material, as expected from its ionization timescale.

astro-ph.HE↗

arXiv2010

White dwarf masses in intermediate polars observed with the Suzaku satellite

Context. White dwarfs (WDs) in cataclysmic variables (CVs) are important experimental laboratories where the electron degeneracy is taking place on a macroscopic scale. Magnetic CVs increase in number especially in the hard X-ray band (>10 keV) thanks to sensitive hard X-ray missions. Aims. From X-ray spectroscopy, we estimate the masses of nearby WDs in moderately-magnetized CVs, or Intermediate Polars (IPs). Methods. Using the Suzaku satellite, we aquired wide-band spectra of 17 IPs, covering 3-50 keV. An accretion column model of Suleimanov et al. (2005) and an optically-thin thermal emission code were used to construct a spectral emission model of IPs with resolved Fe emission lines. By simultaneously fitting the Fe line complex and the hard X-ray continuum of individual spectra, the shock temperature and the WD mass were determined with a better accuracy than in previous studies. Results. We determined the WD masses of the 17 IPs with statistical fitting errors of ~0.1-0.2 Msun in many cases. The WD mass of a recently-found IP, IGR J17195-4100, was also estimated for the first time (1.03+0.24-0.22 Msun). The average WD mass of the sample is 0.88 \pm 0.25 Msun. When our results were compared with previous X-ray mass determinations, we found significant deviation in a few systems although the reason of this is unclear. The iron abundance of the accreting gas was also estimated, and confirmed the previously reported sub-solar tendency in all sources with better accuracy.

astro-ph.HE↗

arXiv2009

Suzaku X-Ray Study of an Anomalous Source XSS J12270-4859

We report the results of the Suzaku X-ray observation of XSS J12270-4859, one of the hard X-ray sources in the INTEGRAL catalogue. The object has been classified as an intermediate polar (IP) by optical spectra and a putative X-ray period of ~860 s. With a 30 ks exposure of Suzaku, we obtained a well-exposed spectrum in the 0.2-70 keV band. We conclude against the previous IP classification based on the lack of Fe Ka emission features in the spectrum and the failure to confirm the previously reported X-ray period. Instead, the X-ray light curve is filled with exotic phenomena, including repetitive flares lasting ~100 s, occasional dips with no apparent periodicities, spectral hardening after some flares, and bimodal changes pivoting between quiet and active phases. The rapid flux changes, the dips, and the power-law spectrum point toward the interpretation that this is a low-mass X-ray binary. Some temporal characteristics are similar to those in the Rapid Burster and GRO J1744-28, making XSS J12270-4859 a very rare object.

astro-ph.HE↗

arXiv2009

The Nature of a Cosmic-Ray Accelerator, CTB37 B, Observed with Suzaku and Chandra

We report on Suzaku and Chandra observations of the young supernova remnant CTB37B, from which TeV gamma-rays were detected by the H.E.S.S. Cherenkov telescope. The 80 ks Suzaku observation provided us with a clear image of diffuse emission and high-quality spectra. The spectra revealed that the diffuse emission is comprised of thermal and non-thermal components. The thermal component can be represented by an NEI model with a temperature, a pre-shock electron density and an age of 0.9(0.7-1.1) keV, 0.4(0.3-0.5) cm^{-3} and 650(350-3150) yr, respectively. This suggests that the explosion of CTB37B occurred in a low-density space. A non-thermal power-law component was found from the southern region of CTB37B. Its photon index of ~1.5 and a high roll-off energy (>15 keV) indicate efficient cosmic-ray acceleration. A comparison of this X-ray spectrum with the TeV gamma-ray spectrum leads us to conclude that the TeV gamma-ray emission seems to be powered by either multi-zone Inverse Compton scattering or the decay of neutral pions. The point source resolved by Chandra near the shell is probably associated with CTB37B, because of the common hydrogen column density with the diffuse thermal emission. Spectral and temporal characteristics suggest that this source is a new anomalous X-ray pulsar.

astro-ph↗

arXiv2009

Super-hard X-Ray Emission from eta Carinae Observed with Suzaku

We present the Suzaku results of eta Carinae in the 5--50 keV range conducted twice around the apastron in 2005 August for 50 ks and in 2006 February for 20 ks. The X-ray Imaging Spectrometer (XIS) produced hard (5--12 keV) band spectra, resolving K shell lines from highly ionized Fe and Ni. The Hard X-ray Detector yielded a significant detection in the super-hard (15--50 keV) band, which is uncontaminated by near-by sources. We constrained the temperature of the optically-thin thermal plasma emission dominant in the hard band as 3--4 keV using the K-shell line features with the XIS. We found significant excess emission above the thermal emission in the super-hard band with the PIN, confirming the previous INTEGRAL ISGRI report. The entire 5--50 keV spectra were fitted by a combination of a thermal plasma model plus a flat power-law or a very hot thermal bremsstrahlung model for the excess emission. No significant change of the excess emission was found at different epochs within the systematic and statistical uncertainties and no flare-like flux amplification was seen in the hard band, indicating that the excess emission is a steady phenomenon. We argue that the super-hard emission is attributable to the inverse Compton of stellar UV photons by non-thermal electrons or to the thermal bremsstrahlung of very hot plasma, and not to the bremsstrahlung by non-thermal electrons colliding with cold ambient matter.

astro-ph.SR↗

arXiv2008

The Suzaku Observations of SS Cygni in Quiescence and Outburst

We present results from the Suzaku observations of the dwarf nova SS Cyg in quiescence and outburst in 2005 November. Owing to high sensitivity of the HXD PIN detector and high spectral resolution of the XIS, we have determined parameters of the plasma with unprecedented precision. The maximum temperature of the plasma in quiescence 20.4 +4.0-2.6 (stat.) +/- 3.0 (sys.) keV is significantly higher than that in outburst 6.0 +0.2-1.3 keV. The elemental abundances are close to the solar ones for the medium-Z elements (Si, S, Ar) whereas they decline both in lighter and heavier elements. Those of oxygen and iron are 0.46 and 0.37 solar, respectively. That of carbon is exceptionally high and 2 solar at least. The solid angle of the reflector subtending over the optically thin thermal plasma is Omega/2π= 1.7+/-0.2 (stat.) +/-0.1 (sys.) in quiescence. A 6.4 keV iron Ka line is resolved into a narrow and broad components. These facts indicate that both the white dwarf and the accretion disk contribute to the continuum reflection and the 6.4 keV iron Ka line. We consider the standard optically thin boundary layer as the most plausible picture for the plasma configuration in quiescence. The solid angle of the reflector in outburst Omega/2π= 0.9 +0.5-0.4 and a broad 6.4 keV iron line indicates that the reflection in outburst originates from the accretion disk and an equatorial accretion belt. From the energy width of the 6.4 keV line, we consider the optically thin thermal plasma in outburst as being distributed on the accretion disk like solar coronae.

astro-ph↗

arXiv2008

Suzaku Observation of Group of Galaxies NGC 507: Temperature and Metal Distributions in the Intra-cluster Medium

Temperature and abundance distributions of the intra-cluster medium (ICM) in the NGC 507 group of galaxies were studied with Suzaku. Observed concentric annular spectra were well-represented by a two temperature model for ICM, and we found steeper abundance gradients for Mg, Si, S, and Fe compared with O in the central region. Abundance ratios of alpha-elements to iron were found to be similar to those in other groups and poor clusters. We calculated metal mass-to-light ratios for Fe, O and Mg (IMLR, OMLR, MMLR) for NGC 507, and values for different systems were compared. Hotter and richer systems tend to show higher values of IMLR, OMLR, and MMLR. OMLR and MMLR were measured to an outer region for the first time with Suzaku, while IMLR was consistent with that with ASCA. We also looked into 2-dimensional map of the hardness ratio, but found no significant deviation from the circular symmetry.

astro-ph↗

arXiv2008

Chandra HETG line spectroscopy of the Non-magnetic Cataclysmic Variable SS Cyg

We present {\it Chandra} HETG observations of SS Cygni in quiescence and outburst. The spectra are characterized by He-like and H-like Ka emission lines from O to Fe, as well as L-shell emission lines from Fe. In quiescence, the spectra are dominated by the H-like Ka lines, whereas in outburst the He-like lines are as intense as the H-like lines. In outburst, the H-like Ka lines from O to Si are broad, with widths of 4--14 eV in Gaussian $σ$ (1800--2300$ {\rm km s^{-1}}$). The large line widths, together with line profiles, indicate that the line-emitting plasma is associated with the Keplerian disk and still retains the azimuthal bulk motion. In quiescence, the emission lines are narrower, with a Gaussian $σ$ of 1--3 eV (420--620$ {\rm km s^{-1}}$). A slightly larger velocity for lighter elements suggests that the lines in quiescence are emitted from an ionizing plasma at the entrance of the boundary layer, where the bulk motion of the optically thick accretion disk is converted into heat due to friction. Using the line intensity ratio of He-like and H-like Ka lines for each element, we have also investigated the temperature distribution in the boundary layer both in quiescence and outburst. The distribution of SS Cyg is found to be consistent with other dwarf novae investigated systematically with {\it ASCA} data.

astro-ph↗

arXiv2008

Restoring the Suzaku Source Position Accuracy and Point-Spread Function

We present an empirical correction of sky coordinates of X-ray photons obtained with the XIS aboard the Suzaku satellite to improve the source position accuracy and restore the point-spread function (PSF). The XIS images are known to have an uncertainty in position of up to 1 arcmin, and to show considerable degradations of the PSF. These problems are caused by a drifting of the satellite attitude due to thermal distortion of the side panel 7, where the attitude control system is mounted. We found that the position error averaged over a pointing observation can be largely reduced by using the relation between the deviation of the source position in the DETX direction and the ecliptic latitude of the pointing target. We parameterized the wobbling of the source position synchronized with the satellite orbital period with temperatures of onboard radiators and elapsed time since the night-day transition of the spacecraft. We developed software, aeattcor, to correct the image drift using these parameters, and applied it to 27 point-source images. We show that the radius of the 90% error circle of the source position was reduced to 19 arcsec and the PSF was sharpened. These improvements have enhanced the scientific capability of the Suzaku XIS.

astro-ph↗