arXiv subjects

Madoka Kawaharada

Publications and source records attributed to Madoka Kawaharada.

At least 19 recordsLinked to original sources

arXiv2020

Origin of the in-orbit instrumental background of the Hard X-ray Imager onboard Hitomi

Understanding and reducing the in-orbit instrumental backgrounds are essential to achieving high sensitivity in hard X-ray astronomical observations. The observational data of the Hard X-ray Imager (HXI) on board the Hitomi satellite provides useful information on the background components, owing to its multi-layer configuration with different atomic numbers: the HXI consists of a stack of four layers of Si (Z = 14) detectors and one layer of CdTe (Z = 48, 52) detector surrounded by well-type BGO (Bi4Ge3O12) active shields. Based on the observational data, the backgrounds of top Si layer, the three underlying Si layers, and the CdTe layer are inferred to be dominated by different components, namely, low-energy electrons, albedo neutrons, and proton-induced radioactivation, respectively. Monte Carlo simulations of the in-orbit background of the HXI reproduce the observed background spectrum of each layer well, thereby verifying the above hypothesis quantitatively. In addition, we suggest the inclusion of an electron shield to reduce the background.

astro-ph.IM↗

arXiv2020

Implications of the mild gas motion found with Hitomi in the core of the Perseus cluster

Based mainly on X-ray observations, studies are made on interactions between the intra-cluster medium (ICM) in clusters of galaxies and their member galaxies. Through (magneto)hydrodynamic and gravitational channels, the moving galaxies are expected to drag the ICM around them, and transfer to the ICM some fraction of their dynamical energies on cosmological time scales. This hypothesis is in line with several observations, including the possible cosmological infall of galaxies towards the cluster center, found over redshifts of z~1 to z~0. Further assuming that the energy lost by the galaxies is first converted into ICM turbulence and then dissipated, this picture can explain the subsonic and uniform ICM turbulence, measured with Hitomi in the core region of the Perseus cluster. The scenario may also explain several other unanswered problems regarding clusters of galaxies, including what prevents the ICM from the expected radiative cooling, how the various mass components in nearby clusters have attained different radial distributions, and how a thermal stability is realized between hot and cool ICM components that co-exist around cD galaxies. This view is also considered to pertain to the general scenario of galaxy evolution, including their environmental effects.

astro-ph.GA↗

arXiv2018

Modeling of proton-induced radioactivation background in hard X-ray telescopes: Geant4-based simulation and its demonstration by Hitomi's measurement in a low Earth orbit

Hard X-ray astronomical observatories in orbit suffer from a significant amount of background due to radioactivation induced by cosmic-ray protons and/or geomagnetically trapped protons. Within the framework of a full Monte Carlo simulation, we present modeling of in-orbit instrumental background dominated by radioactivation. To reduce the computation time required by straightforward simulations of delayed emissions from activated isotopes, we insert a semi-analytical calculation that converts production probabilities of radioactive isotopes by interaction of the primary protons into decay rates at measurement time of all secondary isotopes. Therefore, our simulation method is separated into three steps: (1) simulation of isotope production, (2) semi-analytical conversion to decay rates, and (3) simulation of decays of the isotopes at measurement time. This method is verified by a simple setup that has a CdTe semiconductor detector, and shows a 100-fold improvement in efficiency over the straightforward simulation. The simulation framework was tested against data measured with a CdTe sensor in the Hard X-ray Imager onboard the Hitomi X-ray Astronomy Satellite, which was put into a low Earth orbit with an altitude of 570 km and an inclination of 31 degrees, and thus experienced a large amount of irradiation from geomagnetically trapped protons during its passages through the South Atlantic Anomaly. The simulation is able to treat full histories of the proton irradiation and multiple measurement windows. The simulation results agree very well with the measured data, showing that the measured background is well described by the combination of proton-induced radioactivation of the CdTe detector itself and thick Bi4Ge3O12 scintillator shields, leakage of cosmic X-ray background and albedo gamma-ray radiation, and emissions from naturally contaminated isotopes in the detector system.

astro-ph.IM↗

arXiv2017

Hitomi constraints on the 3.5 keV line in the Perseus galaxy cluster

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

astro-ph.HE↗

arXiv2016

The Quiescent Intracluster Medium in the Core of the Perseus Cluster

Clusters of galaxies are the most massive gravitationally-bound objects in the Universe and are still forming. They are thus important probes of cosmological parameters and a host of astrophysical processes. Knowledge of the dynamics of the pervasive hot gas, which dominates in mass over stars in a cluster, is a crucial missing ingredient. It can enable new insights into mechanical energy injection by the central supermassive black hole and the use of hydrostatic equilibrium for the determination of cluster masses. X-rays from the core of the Perseus cluster are emitted by the 50 million K diffuse hot plasma filling its gravitational potential well. The Active Galactic Nucleus of the central galaxy NGC1275 is pumping jetted energy into the surrounding intracluster medium, creating buoyant bubbles filled with relativistic plasma. These likely induce motions in the intracluster medium and heat the inner gas preventing runaway radiative cooling; a process known as Active Galactic Nucleus Feedback. Here we report on Hitomi X-ray observations of the Perseus cluster core, which reveal a remarkably quiescent atmosphere where the gas has a line-of-sight velocity dispersion of 164+/-10 km/s in a region 30-60 kpc from the central nucleus. A gradient in the line-of-sight velocity of 150+/-70 km/s is found across the 60 kpc image of the cluster core. Turbulent pressure support in the gas is 4% or less of the thermodynamic pressure, with large scale shear at most doubling that estimate. We infer that total cluster masses determined from hydrostatic equilibrium in the central regions need little correction for turbulent pressure.

astro-ph.GA↗

arXiv2016

Suzaku observation of a high entropy cluster Abell 548W

Abell 548W, one of the galaxy clusters located in the Abell 548 region, has about an order of magnitude lower X-ray luminosity compared to ordinal clusters in view of the well known intracluster medium (ICM) temperature vs X-ray luminosity (kT-L_X) relation. The cluster hosts a pair of diffuse radio sources to the north west and north, both about 10' apart from the cluster center. They are candidate radio relics, frequently associated with merging clusters. A Suzaku deep observation with exposure of 84.4 ks was performed to search signatures for merging in this cluster. The XIS detectors successfully detected the ICM emission out to 16' from the cluster center. The temperature is ~3.6 keV around its center, and ~2 keV at the outermost regions. The hot region (~6 keV) aside the relic candidates shifted to the cluster center reported by XMM-Newton was not seen in the Suzaku data, although its temperature of 3.6 keV itself is higher than the average temperature of 2.5 keV around the radio sources. In addition, a signature of a cool (kT ~0.9 keV) component was found around the north west source. A marginal temperature jump at its outer-edge was also found, consistent with the canonical idea of shock acceleration origin of the radio relics. The cluster has among the highest central entropy of ~400 keV cm^2 and is one of the so-called low surface brightness clusters. Taking into account the fact that its shape itself is relatively circular and smooth and also its temperature structure is nearly flat, possible scenarios for merging is discussed.

astro-ph.HE↗

arXiv2016

Galaxy Infall by Interacting with its Environment: a Comprehensive Study of 340 Galaxy Clusters

To study systematically the evolution on the angular extents of the galaxy, ICM, and dark matter components in galaxy clusters, we compiled the optical and X-ray properties of a sample of 340 clusters with redshifts $<0.5$, based on all the available data with the Sloan Digital Sky Survey (SDSS) and {\it Chandra}/{\it XMM-Newton}. For each cluster, the member galaxies were determined primarily with photometric redshift measurements. The radial ICM mass distribution, as well as the total gravitational mass distribution, were derived from a spatially-resolved spectral analysis of the X-ray data. When normalizing the radial profile of galaxy number to that of the ICM mass, the relative curve was found to depend significantly on the cluster redshift; it drops more steeply towards outside in lower redshift subsamples. The same evolution is found in the galaxy-to-total mass profile, while the ICM-to-total mass profile varies in an opposite way. We interpret that the galaxies, the ICM, and the dark matter components had similar angular distributions when a cluster was formed, while the galaxies travelling interior of the cluster have continuously fallen towards the center relative to the other components, and the ICM has slightly expanded relative to the dark matter although it suffers strong radiative loss. This cosmological galaxy infall, accompanied by an ICM expansion, can be explained by considering that the galaxies interact strongly with the ICM while they are moving through it. The interaction is considered to create a large energy flow of $10^{44-45}$ erg $\rm s^{-1}$ per cluster from the member galaxies to their environment, which is expected to continue over cosmological time scales.

astro-ph.GA↗

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↗

arXiv2013

Metals in the Intracluster Medium of MS 1512.4+3647 Observed with Suzaku: Implications for the Metal Enrichment History

The cluster of galaxies MS 1512.4+3647 (z=0.372) was observed with Suzaku for 270 ks. Besides the Fe abundance, the abundances of Mg, Si, S, and Ni are separately determined for the first time in a medium redshift cluster (z>0.3). The derived abundance pattern of MS 1512.4+3647 is consistent with those of nearby clusters, suggesting that the system has similar contributions from supernovae (SNe) Ia and SNe II to nearby clusters. The number ratio of SNe II to SNe Ia is $\sim3$. The estimated total numbers of both SNe II and SNe Ia against gas mass indicate similar correlation with those for the nearby clusters. The abundance results of MS 1512.4+3647 is consistent with the standard scenario that the SN II rate history roughly follows the star-formation history which has a peak at 1<z<2 and then declines by about one order of magnitude toward $z\sim0$. The similar number of SNe Ia to the nearby clusters suggests that the SN Ia rate declines steeply from z=0.37 to z=0 and/or SN Ia explosions occurred predominantly at larger redshifts.

astro-ph.CO↗

arXiv2013

Probing of the Interactions Between the Hot Plasmas and Galaxies in Clusters from z=0.1 to 0.9

Based on optical and X-ray data for a sample of 34 relaxed rich clusters of galaxies with redshifts of 0.1-0.9, we studied relative spatial distributions of the two major baryon contents, the cluster galaxies and the hot plasmas. Using multi-band photometric data taken with the UH88 telescope, we determined the integrated (two dimensional) radial light profiles of member galaxies in each cluster using two independent approaches, i.e., the background subtraction and the color-magnitude filtering. The ICM mass profile of each cluster in our sample, also integrated in two dimensions, was derived from a spatially-resolved spectral analysis using XMM-Newton and Chandra data. Then, the radially-integrated light profile of each cluster was divided by its ICM mass profile, to obtain a profile of "galaxy light vs. ICM mass ratio". The ratio profiles over the central 0.65 R500 regions were found to steepen from the higher- to lower- redshift subsamples, meaning that the galaxies become more concentrated in the ICM sphere towards lower redshifts. The evolution is also seen in galaxy number vs. ICM mass ratio profiles. A range of systematic uncertainties in the galaxy light measurements, as well as many radius-/redshift- dependent biases to the galaxy vs. ICM profiles have been assessed, but none of them is significant against the observed evolution. Besides, the galaxy light vs. total mass ratio profiles also exhibit gradual concentration towards lower redshift. We interpret in the context that the galaxies, the ICM, and the dark matter components followed a similar spatial distribution in the early phase (z>0.5), while the galaxies have fallen towards the center relative to the others at a later phase.

astro-ph.CO↗

arXiv2013

Suzaku observations of Abell 1835 outskirts: Deviation from hydrostatic equilibrium

We present results of four-pointing Suzaku X-ray observations (total ~200 ks) of the intracluster medium (ICM) in the Abell 1835 galaxy cluster (kT ~ 8 keV, z = 0.253) out to the virial radius (r_vir ~ 2.9 Mpc) and beyond. Faint X-ray emission from the ICM out to r_vir is detected. The temperature gradually decreases with radius from ~8 keV in the inner region to ~2 keV at r_vir. The entropy profile is shown to flatten beyond r_500, in disagreement with the r_1.1 dependence predicted from the accretion shock heating model. The thermal pressure profile in the range 0.3r_500 < r < r_vir agrees well with that obtained from the stacked Sunyaev-Zel'dovich effect observations with the Planck satellite. The hydrostatic mass profile in the cluster outskirts (r_500 < r < r_vir) falls well short of the weak lensing one derived from Subaru/Suprime-Cam observations, showing an unphysical decrease with radius. The gas mass fraction at r_vir defined with the lensing total mass agrees with the cosmic baryon fraction from the WMAP 7-year data. All these results indicate, rather than the gas-clumping effect, that the bulk of the ICM in the cluster outskirts is far from hydrostatic equilibrium and infalling matter retained some of its kinetic energy. Finally, combining with our recent Suzaku and lensing analysis of Abell 1689, a cluster of similar mass, temperature, and redshift, we show that the cluster temperature distribution in the outskirts is significantly correlated with the galaxy density field in the surrounding large-scale environment at (1-2)r_vir.

astro-ph.CO↗

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 observations of the Hydra A cluster out to the virial radius

We report Suzaku observations of the northern half of the Hydra A cluster out to ~1.4 Mpc, reaching the virial radius. This is the first Suzaku observations of a medium-size (kT ~3 keV) cluster out to the virial radius. Two observations were conducted, north-west and north-east offsets, which continue in a filament direction and a void direction of the large-scale structure of the Universe, respectively. The X-ray emission and distribution of galaxies elongate in the filament direction. The temperature profiles in the two directions are mostly consistent with each other within the error bars and drop to 1.5 keV at 1.5 r_500. As observed by Suzaku in hot clusters, the entropy profile becomes flatter beyond r_500, in disagreement with the r^1.1 relationship that is expected from accretion shock heating models. When scaled with the average intracluster medium (ICM) temperature, the entropy profiles of clusters observed with Suzaku are universal and do not depend on system mass. The hydrostatic mass values in the void and filament directions are in good agreement, and the Navarro, Frenk, and White universal mass profile represents the hydrostatic mass distribution up to ~ 2 r_500. Beyond r_500, the ratio of gas mass to hydrostatic mass exceeds the result of the Wilkinson microwave anisotropy probe, and at r_100, these ratios in the filament and void directions reach 0.4 and 0.3, respectively. We discuss possible deviations from hydrostatic equilibrium at cluster outskirts. We derived radial profiles of the gasmass- to-light ratio and iron-mass-to-light ratio out to the virial radius. Within r_500, the iron-mass-to-light ratio of the Hydra A cluster was compared with those in other clusters observed with Suzaku.

astro-ph.CO↗

arXiv2012

Two-Phase ICM in the Central Region of the Rich Cluster of Galaxies Abell 1795: A Joint Chandra, XMM-Newton, and Suzaku View

Based on a detailed analysis of the high-quality Chandra, XMM-Newton, and Suzaku data of the X-ray bright cluster of galaxies Abell 1795, we report clear evidence for a two-phase intracluster medium (ICM) structure, which consists of a cool (with a temperature T = 2.0-2.2 keV) and a hot (T = 5.0-5.7 keV) component that coexist and dominate the X-ray emission at least in the central 80 kpc. A third weak emission component (T = 0.8 keV) is also detected within the innermost 144 kpc and is ascribed to a portion of inter-stellar medium (ISM) of the cD galaxy. Deprojected spectral analysis reveals flat radial temperature distributions for both the hot phase and cool phase components. These results are consistent with the ASCA measurements reported in Xu et al. (1998), and resemble the previous findings for the Centaurus cluster (e.g., Takahashi et al. 2009). By analyzing the emission measure ratio and gas metal abundance maps created from the Chandra data, we find that the cool phase component is more metal-enriched than the hot phase one in 50-100 kpc region, which agrees with that found in M87 (Simionescu et al. 2008). The coexistence of the cool phase and hot phase ICM cannot be realized by bubble uplifting from active galactic nuclei (AGN) alone. Instead, the two-phase ICM properties are better reconciled with a cD corona model (Makishima et al. 2001). (Abridged)

astro-ph.HE↗

arXiv2011

Suzaku and XMM-Newton Observations of the Fornax cluster: Temperature and Metallicity Distribution

Suzaku observed a central region and five offset regions within 0.2 r180 in the Fornax cluster, a nearby poor cluster, and XMM-Newton mapped the cluster with 15 pointings out to 0.3 r180. The distributions of O, Mg, Si, S, and Fe in the intracluster medium (ICM) were studied with Suzaku, and those of Fe and temperature were studied with XMM. The temperature of the ICM gradually decreases with radius from 1.3 keV at 0.04 r180 to 1 keV at 0.2-0.3 r180. If the new solar abundances of Lodders et al. (2003) and a single-temperature plasma model are adopted, O, Mg, Si, S, and Fe show similar abundances: 0.4-0.6 solar within 0.02-0.2 r180. This Fe abundance is similar to those at 0.1-0.2 r180 in rich clusters and other groups of galaxies. At 0.2-0.3 r180, the Fe abundance becomes 0.2-0.3 solar. A two-temperature plasma model yields ICM abundances that are higher by a factor of 1.2-1.5, but gives similar abundance ratios among O, Mg, Si, S, and Fe. The northern region has a lower ICM temperature and higher brightness and Fe abundance, whereas the southern region has a higher ICM temperature and lower brightness and Fe abundance. These results indicate that the cD galaxy may have traveled from the north because of recent dynamical evolution. The cumulative oxygen- and iron-mass-to-light ratios within 0.3 r180 are more than an order of magnitude lower than those of rich clusters and some relaxed groups of galaxies. Past dynamical evolution might have hindered the strong concentration of hot gas in the Fornax cluster's central region. Scatter in the IMLR and similarity in the element abundances in the ICM of groups and clusters of galaxies indicate early metal synthesis.

astro-ph.CO↗

arXiv2011

Improvements in calibration of GSO scintillators in the Suzaku Hard X-ray Detector

Improvements of in-orbit calibration of GSO scintillators in the Hard X-ray Detector on board Suzaku are reported. To resolve an apparent change of the energy scale of GSO which appeared across the launch for unknown reasons, consistent and thorough re-analyses of both pre-launch and in-orbit data have been performed. With laboratory experiments using spare hardware, the pulse height offset, corresponding to zero energy input, was found to change by ~0.5 of the full analog voltage scale, depending on the power supply. Furthermore, by carefully calculating all the light outputs of secondaries from activation lines used in the in-orbit gain determination, their energy deposits in GSO were found to be effectively lower, by several percent, than their nominal energies. Taking both these effects into account, the in-orbit data agrees with the on-ground measurements within ~5%, without employing the artificial correction introduced in the previous work (Kokubun et al. 2007). With this knowledge, we updated the data processing, the response, and the auxiliary files of GSO, and reproduced the HXD-PIN and HXD-GSO spectra of the Crab Nebula over 12-300 keV by a broken powerlaw with a break energy of ~110 keV.

astro-ph.IM↗

arXiv2011

Soft and Hard X-Ray Emissions from the Anomalous X-ray Pulsar 4U 0142+61 Observed with Suzaku

The anomalous X-ray pulsar 4U 0142+61 was observed with Suzaku on 2007 August 15 for a net exposure of -100 ks, and was detected in a 0.4 to ~70 keV energy band. The intrinsic pulse period was determined as 8.68878 \pm 0.00005 s, in agreement with an extrapolation from previous measurements. The broadband Suzaku spectra enabled a first simultaneous and accurate measurement of the soft and hard components of this object by a single satellite. The former can be reproduced by two blackbodies, or slightly better by a resonant cyclotron scattering model. The hard component can be approximated by a power-law of photon index Γh ~0.9 when the soft component is represented by the resonant cyclotron scattering model, and its high-energy cutoff is constrained as >180 keV. Assuming an isotropic emission at a distance of 3.6 kpc, the unabsorbed 1-10 keV and 10-70 keV luminosities of the soft and hard components are calculated as 2.8e+35 erg s^{-1} and 6.8e+34 erg s^{-1}, respectively. Their sum becomes ~10^3 times as large as the estimated spin-down luminosity. On a time scale of 30 ks, the hard component exhibited evidence of variations either in its normalization or pulse shape.

astro-ph.HE↗

arXiv2011

Suzaku X-ray Follow-up Observation of Weak-lensing-detected Halos in the Field around ZwCl0823.2+0425

We present the results of Suzaku X-ray follow-up observation of weak-lensing-detected halos in the field around galaxy cluster ZwCl0823.2+0425. We clearly detected X-ray emission associated with most of these halos and determined their detailed physical parameters such as X-ray luminosity, temperature, and metal abundance, for the first time. We find that the X-ray luminosity - temperature relation for these halos agrees with former typical results. With mass determined from the weak gravitational lensing data, the mass-temperature relation for them is also investigated and found to be consistent with the prediction from a simple self-similar model and results of the previous studies with both lensing and X-ray data. We would like to emphasize that the self-similar scaling relation of mass and temperature is shown here for the first time using a weak-lensing selected sample, whereas previous studies of the mass scaling relation used X-ray-selected samples of clusters. Therefore, our study demonstrates importance of X-ray follow-up observations of shear-selected clusters, and shows that a joint X-ray and lensing analysis will be crucial for clusters discovered by the forthcoming weak-lensing surveys, such as the one planned with Subaru/Hyper-Suprime-Cam.

astro-ph.CO↗