arXiv subjects

Madoka Kawaharada

Publications and source records attributed to Madoka Kawaharada.

33 records · Page 2Linked to original sources

arXiv2010

Soft Gamma-ray Detector for the ASTRO-H Mission

ASTRO-H is the next generation JAXA X-ray satellite, intended to carry instruments with broad energy coverage and exquisite energy resolution. The Soft Gamma-ray Detector (SGD) is one of ASTRO-H instruments and will feature wide energy band (40-600 keV) at a background level 10 times better than the current instruments on orbit. SGD is complimentary to ASTRO-H's Hard X-ray Imager covering the energy range of 5-80 keV. The SGD achieves low background by combining a Compton camera scheme with a narrow field-of-view active shield where Compton kinematics is utilized to reject backgrounds. The Compton camera in the SGD is realized as a hybrid semiconductor detector system which consists of silicon and CdTe (cadmium telluride) sensors. Good energy resolution is afforded by semiconductor sensors, and it results in good background rejection capability due to better constraints on Compton kinematics. Utilization of Compton kinematics also makes the SGD sensitive to the gamma-ray polarization, opening up a new window to study properties of gamma-ray emission processes. The ASTRO-H mission is approved by ISAS/JAXA to proceed to a detailed design phase with an expected launch in 2014. In this paper, we present science drivers and concept of the SGD instrument followed by detailed description of the instrument and expected performance.

astro-ph.IM↗

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

Metallicity of the Fossil Group NGC 1550 Observed with Suzaku

We studied the temperature and metal abundance distributions of the intra-cluster medium (ICM) in a group of galaxies NGC 1550 observed with Suzaku. The NGC 1550 is classified as a fossil group, which have few bright member galaxies except for the central galaxy. Thus, such a type of galaxy is important to investigate how the metals are enriched to the ICM. With the Suzaku XIS instruments, we directly measured not only Si, S, and Fe lines but also O and Mg lines and obtained those abundances to an outer region of ~0.5 r_180 for the first time, and confirmed that the metals in the ICM of such a fossil group are indeed extending to a large radius. We found steeper gradients for Mg, Si, S, and Fe abundances, while O showed almost flat abundance distribution. Abundance ratios of alpha-elements to Fe were similar to those of the other groups and poor clusters. We calculated the number ratio of type II to type Ia supernovae for the ICM enrichment to be 2.9 +- 0.5 within 0.1 r_180, and the value was consistent with those for the other groups and poor clusters observed with Suzaku. We also calculated metal mass-to-light ratios (MLRs) for Fe, O and Mg with B-band and K-band luminosities of the member galaxies of NGC 1550. The derived MLRs were comparable to those of NGC 5044 group in the r<0.1 r_180 region, while those of NGC 1550 are slightly higher than those of NGC 5044 in the outer region.

astro-ph.CO↗

arXiv2010

Suzaku Observation of Abell 1689: Anisotropic Temperature and Entropy Distributions Associated with the Large-Scale Structure

(Abridged) We present results of Suzaku observations of the intracluster medium (ICM) in Abell 1689, combined with complementary analysis of the SDSS data and weak and strong lensing analysis of Subaru/Suprime-Cam and HST/ACS observations. Faint X-ray emission from the ICM around the virial radius is detected at 4.0 sigma significance. We find anisotropic gas temperature and entropy distributions in cluster outskirts correlated with large-scale structure of galaxies. The high temperature and entropy region in the northeastern (NE) outskirts is connected to an overdense filamentary structure. The outskirt regions in contact with low density void environments have low gas temperatures and entropies, deviating from hydrostatic equilibrium. These results suggest that thermalization of the ICM occurs faster along the filamentary structures than the void regions. A joint X-ray and lensing analysis shows that the hydrostatic mass is $\sim60-90%$ of spherical lensing one but comparable to a triaxial halo mass within errors in $0.6r_{2500} \simlt r \simlt 0.8r_{500}$, and that it is significantly biased as low as $\simlt60%$ within $0.4r_{2500}$, irrespective of mass models. The thermal gas pressure within $r_{500}$ is, at most, $\sim50$--60% of the total pressure to balance fully the gravity of the spherical lensing mass, and $\sim30$--40% around the virial radius. Although these constitute lower limits when one considers the possible halo triaxiality, these small relative contributions of thermal pressure would require additional sources of pressure, such as bulk and/or turbulent motions.

astro-ph.CO↗

arXiv2009

Suzaku Constraints on the Soft and Hard Excess Emissions from Abell 2199

The nearby ($z=0.03015$) cluster of galaxies Abell~2199 was observed by Suzaku in X-rays, with five pointings for $\sim 20$ ks each. From the XIS data, the temperature and metal abundance profiles were derived out to $\sim 700$ kpc (0.4 times virial radius). Both these quantities decrease gradually from the center to peripheries by a factor of $\sim 2$, while the oxygen abundance tends to be flat. The temperature within 12' ($\sim 430$ kpc) is $\sim 4$ keV, and the 0.5--10 keV X-ray luminosity integrated up to 30' is $(2.9 \pm 0.1) \times 10^{44}$ erg s$^{-1}$, in agreement with previous XMM-Newton measurements. Above this thermal emission, no significant excess was found either in the XIS range below $\sim 1$ keV, or in the HXD-PIN range above $\sim 15$ keV. The 90%-confidence upper limit on the emission measure of an assumed 0.2 keV warm gas is (3.7--7.5) $\times 10^{62}$ cm$^{-3}$ arcmin$^{-2}$, which is 3.7--7.6 times tighter than the detection reported with XMM-Newton. The 90%-confidence upper limit on the 20--80 keV luminosity of any power law component is $1.8 \times 10^{43}$ erg s$^{-1}$, assuming a photon index of 2.0. Although this upper limit does not reject the possible 2.1$σ$ detection by the BeppoSAX PDS, it is a factor of 2.1 tighter than that of the PDS if both are considered upper limits. The non-detection of the hard excess can be reconciled with the upper limit on diffuse radio emission, without invoking the very low magnetic fields ($< 0.073 μ$G) which were suggested previously.

astro-ph.CO↗

arXiv2009

Suzaku Observations of Abell 1795: Cluster Emission to R_200

We report Suzaku observations of the galaxy cluster Abell 1795 that extend to r_200 ~ 2 Mpc, the radius within which the mean cluster mass density is 200 times the cosmic critical density. These observations are the first to probe the state of the intracluster medium in this object at r > 1.3 Mpc. We sample two disjoint sectors in the cluster outskirts (1.3 < r < 1.9 Mpc) and detect X-ray emission in only one of them to a limiting (3-sigma) soft X-ray surface brightness of B(0.5-2 keV) = 1.8 x 10^-12 erg s^-1 cm^-2 deg^-2, a level less than 20% of the cosmic X-ray background brightness. We trace the run of temperature with radius at r > 0.4 Mpc and find that it falls relatively rapidly (T ~ r^-0.9), reaching a value about one third of its peak at the largest radius we can measure it. Assuming the intracluster medium is in hydrostatic equilibrium and is polytropic, we find a polytropic index of 1.3 +0.3-0.2 and we estimate a mass of 4.1 +0.5-0.3 x 10^14 M_solar within 1.3 Mpc, somewhat (2.7-sigma) lower than that reported by previous observers. However, our observations provide evidence for departure from hydrostatic equilibrium at radii as small as r ~ 1.3 Mpc ~ r_500 in this apparently regular and symmetrical cluster.

astro-ph.CO↗

arXiv2009

A Galaxy Merger Scenario for the NGC 1550 Galaxy from Metal Distributions in the X-ray Emitting Plasma

The elliptical galaxy NGC 1550 at a redshift of $z=0.01239$, identified with an extended X-ray source RX J0419+0225, was observed with {\it XMM-Newton} for 31 ks. From the X-ray data and archival near infra-red data of Two Micron All Sky survay, we derive the profiles of components constituting the NGC 1550 system; the gas mass, total mass, metal mass, and galaxy luminosity. The metals (oxygen, silicon, and iron) are extended to $\sim 200$ kpc from the center, wherein $\sim$ 70% of the $K$-band luminosity is carried by NGC 1550 itself. As first revealed with {\it ASCA}, the data reconfirms the presence of a dark halo, of which the mass ($1.6 \times 10^{13} M_{\odot}$) is typical of a galaxy group rather than of a single galaxy. Within 210 kpc, the $K$-band mass-to-light ratio reaches $75 M_{\odot}/L_{\odot}$, which is comparable to those of clusters of galaxies. The iron-mass-to-light ratio profile (silicon- and oxygen mass-to-light ratio profiles as well) exhibits about two orders of magnitude decrease toward the center. Further studies comparing mass densities of metals with those of the other cluster components reveal that the iron (as well as silicon) in the ICM traces very well the total gravitating mass, whereas the stellar component is significantly more concentrated to within several tens kpc of the NGC 1550 nucleus. Thus, in the central region, the amount of metals is significantly depleted for the luminous galaxy light. Among a few possible explanations of this effect, the most likely scenario is that galaxies in this system were initially much more extended than today, and gradually fell to the center and merged into NGC 1550.

astro-ph.CO↗

arXiv2009

Modeling and Reproducibility of Suzaku HXD PIN/GSO Background

Suzaku Hard X-ray Detector (HXD) achieved the lowest background level than any other previously or currently operational missions sensitive in the energy range of 10--600 keV, by utilizing PIN photodiodes and GSO scintillators mounted in the BGO active shields to reject particle background and Compton-scattered events as much as possible. Because it does not have imaging capability nor rocking mode for the background monitor, the sensitivity is limited by the reproducibility of the non X-ray background (NXB) model. We modeled the HXD NXB, which varies with time as well as other satellites with a low-earth orbit, by utilizing several parameters, including particle monitor counts and satellite orbital/attitude information. The model background is supplied as an event file in which the background events are generated by random numbers, and can be analyzed in the same way as the real data. The reproducibility of the NXB model depends on the event selection criteria (such as cut-off rigidity and energy band) and the integration time, and the 1sigma systematic error is estimated to be less than 3% (PIN 15--40 keV) and 1% (GSO 50--100 keV) for more than 10 ksec exposure.

astro-ph.IM↗

arXiv2008

Hard X-ray Properties of the Merging Cluster Abell 3667 as Observed with Suzaku

Wide-band Suzaku data on the merging cluster Abell 3667 were examined for hard X-ray emission in excess to the known thermal component. Suzaku detected X-ray signals in the wide energy band from 0.5 to 40 keV. The hard X-ray (> 10 keV) flux observed by the HXD around the cluster center cannot be explained by a simple extension of the thermal emission with average temperature of ~7 keV. The emission is most likely an emission from a very hot (kT > 13.2 keV) thermal component around the cluster center, produced via a strong heating process in the merger. In the north-west radio relic, no signature of non-thermal emission was observed. Using the HXD, the overall upper-limit flux within a 34'x34' field-of-view around the relic is derived to be 5.3e-12 erg s-1 cm-2 in the 10-40 keV band, after subtracting the ICM contribution estimated using the XIS or the XMM-Newton spectra. Directly on the relic region, the upper limit is further tightened by the XIS data to be less than 7.3e-13 erg s-1 cm-2, when converted into the 10--40 keV band. The latter value suggest that the average magnetic field within the relic is higher than 1.6 uG. The non-thermal pressure due to magnetic fields and relativistic electrons may be as large as ~20% of the thermal pressure in the region.

astro-ph↗

arXiv2008

Spectral transitions of an ultraluminous X-ray source, NGC 2403 Source 3

Suzaku observation of an ultraluminous X-ray source, NGC 2403 Source 3, performed on 2006 March 16--17, is reported. The Suzaku XIS spectrum of Source 3 was described with a multi-color black-body-like emission from an optically thick accretion disk. The innermost temperature and radius of the accretion disk was measured to be $T_{\rm in} = 1.08_{-0.03}^{+0.02} $ keV and $R_{\rm in} = 122.1_{-6.8}^{+7.7} α^{1/2}$ km, respectively, where $α= (\cos 60^\circ /\cos i)$ with $i$ being the disk inclination. The bolometric luminosity of the source was estimated to be $L_{\rm bol} = 1.82 \times 10^{39} α$ ergs s$^{-1}$. Archival Chandra and XMM-Newton data of the source were analyzed for long-term spectral variations. In almost all observations, the source showed multi-color black-body-like X-ray spectra with parameters similar to those in the Suzaku observation. In only one Chandra observation, however, Source 3 was found to exhibit a power-law-like spectrum, with a photon index of $Γ= 2.37 \pm 0.08$, when it was fainter by about $\sim 15 %$ than in the Suzaku observation. The spectral behavior is naturally explained in terms of a transition between the slim disk state and the "very high" states, both found in Galactic black hole binaries when their luminosity approach the Eddington limit. These results are utilized to argue that ultraluminous X-ray sources generally have significantly higher black-hole masses than ordinary stellar-mass black holes.

astro-ph↗

arXiv2007

Suzaku Observation of the Anomalous X-ray Pulsar CXOU J164710.2--455216

Suzaku TOO observation of the anomalous X-ray pulsar CXOU J164710.2-455216 was performed on 2006 September 23--24 for a net exposure of 38.8 ks. During the observation, the XIS was operated in 1/8 window option to achieve a time resolution of 1 s. Pulsations are clearly detected in the XIS light curves with a barycenter corrected pulse period of 10.61063(2) s. The XIS pulse profile shows 3 peaks of different amplitudes with RMS fractional amplitude of ~11% in 0.2--6.0 keV energy band. Though the source was observed with the HXD of Suzaku, the data is highly contaminated by the nearby bright X-ray source GX 340+0 which was in the HXD field of view. The 1-10 keV XIS spectra are well fitted by two blackbody components. The temperatures of two blackbody components are found to be 0.61+/-0.01 keV and 1.22+/-0.06 keV and the value of the absorption column density is 1.73+/-0.03 x 10^{22} atoms cm^{-2}. The observed source flux in 1-10 keV energy range is calculated to be 2.6 x 10^{-11} ergs cm^{-2} s^{-1} with significant contribution from the soft blackbody component (kT = 0.61 keV). Pulse phase resolved spectroscopy of XIS data shows that the flux of the soft blackbody component consists of three narrow peaks, whereas the flux of the other component shows a single peak over the pulse period of the AXP. The blackbody radii changes between 2.2-2.7 km and 0.28-0.38 km (assuming the source distance to be 5 kpc) over pulse phases for the soft and hard components, respectively. The details of the results obtained from the timing and spectral analysis is presented.

astro-ph↗

arXiv2007

In Orbit Timing Calibration of the Hard X-Ray Detector on Board Suzaku

The hard X-ray detector (HXD) on board the X-ray satellite Suzaku is designed to have a good timing capability with a 61 $μ$s time resolution. In addition to detailed descriptions of the HXD timing system, results of in-orbit timing calibration and performance of the HXD are summarized. The relative accuracy of time measurements of the HXD event was confirmed to have an accuracy of $1.9\times 10^{-9}$ s s$^{-1}$ per day, and the absolute timing was confirmed to be accurate to 360 $μ$s or better. The results were achieved mainly through observations of the Crab pulsar, including simultaneous ones with RXTE, INTEGRAL, and Swift.

astro-ph↗

arXiv2007

Suzaku Observation of HCG 62: Temperature, Abundance, and Extended Hard X-ray Emission Profiles

We present results of 120 ks observation of a compact group of galaxies HCG~62 ($z=0.0145$) with Suzaku XIS and HXD-PIN\@. The XIS spectra for four annular regions were fitted with two temperature {\it vapec} model with variable abundance, combined with the foreground Galactic component. The Galactic component was constrained to have a common surface brightness among the four annuli, and two temperature {\it apec} model was preferred to single temperature model. We confirmed the multi-temperature nature of the intra-group medium reported with Chandra and XMM-Newton, with a doughnut-like high temperature ring at radii 3.3--6.5$'$ in a hardness image. We found Mg, Si, S, and Fe abundances to be fairly robust. We examined the possible ``high-abundance arc'' at $\sim 2'$ southwest from the center, however Suzaku data did not confirm it. We suspect that it is a misidentification of an excess hot component in this region as the Fe line. Careful background study showed no positive detection of the extended hard X-rays previously reported with ASCA, in 5--12 keV with XIS and 12--40 keV with HXD-PIN, although our upper limit did not exclude the ASCA result. There is an indication that the X-ray intensity in $r<3.3'$ region is $70\pm 19$% higher than the nominal CXB level (5--12 keV), and Chandra and Suzaku data suggest that most of this excess could be due to concentration of hard X-ray sources with an average photon index of $Γ=1.38\pm 0.06$. Cumulative mass of O, Fe and Mg in the group gas and the metal mass-to-light ratio were derived and compared with those in other groups. Possible role of AGN or galaxy mergers in this group is also discussed.

astro-ph↗

arXiv2007

X-Ray Study of Temperature and Abundance Profiles of the Cluster of Galaxies Abell 1060 with Suzaku

We carried out observations of the central and 20' east offset regions of the cluster of galaxies Abell 1060 with Suzaku. Spatially resolved X-ray spectral analysis has revealed temperature and abundance profiles of Abell 1060 out to 27' ~ 380; /h_70 kpc, which corresponded to ~ 0.25; r_180. Temperature decrease of the intra cluster medium from 3.4 keV at the center to 2.2 keV in the outskirt region are clearly observed. Abundances of Si, S and Fe also decrease by more than 50% from the center to the outer, while Mg shows fairly constant abundance distribution at ~ 0.7 solar within r < 17'. O shows lower abundance of ~ 0.3 solar in the central region (r~ 6'), and indicates a similar feature with Mg, however it is sensitive to the estimated contribution of the Galactic components of kT_1 ~ 0.15 keV and kT_2 ~ 0.7 keV in the outer annuli (r ~ 13'). Systematic effects due to the point spread function tails, contamination on the XIS filters, instrumental background, cosmic and/or Galactic X-ray background, and the assumed solar abundance tables are carefully examined. Results on temperature and abundances of Si, S, and Fe are consistent with those derived by XMM-Newton at r < 13'. Formation and metal enrichment process of the cluster are discussed based on the present results.

astro-ph↗

arXiv2006

Suzaku Observations of the Centaurus Cluster: Absence of Bulk Motions in the Intracluster Medium

The Centaurus cluster (z=0.0104) was observed with the X-ray Imaging Spectrometer (XIS) onboard the Suzaku X-ray satellite in three pointings, one centered on the cluster core and the other two offset by +-8' in declination. To search for possible bulk motions of the intracluster medium, the central energy of He-like Fe-K line (at a rest-frame energy of 6.7 keV) was examined to look for a positional dependence. Over spatial scales of 50 kpc to 140 kpc around the cluster core, the central line energy was found to be constant within the calibration error of 15 eV. The 90% upper limit on the line-of-sight velocity difference is |Delta_v|< 1400 km/s, giving a tighter constraint than previous measurements. The significant velocity gradients inferred from a previous Chandra study were not detected between two pairs of rectangular regions near the cluster core. These results suggest that the bulk velocity does not largely exceed the thermal velocity of the gas in the central region of the Centaurus cluster. The mean redshift of the intracluster medium was determined to be 0.0097, in agreement with the optical redshift of the cluster within the calibration uncertainty. Implications of the present results for the estimation of the cluster mass are briefly discussed.

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