Shota Inoue

Search for a non-equilibrium plasma in the merging galaxy cluster Abell 754

Abell 754 is a galaxy cluster in which an ongoing merger is evident on the plane of the sky, from the southeast to the northwest. We study the spatial variation of the X-ray spectra observed with Suzaku along the merging direction, centering on the Fe Ly-alpha / Fe He-alpha line ratio to search for possible deviation from ionization equilibrium. Fitting with a single temperature collisional non-equilibrium plasma model shows that the electron temperature increases from the southeast to the northwest. The ionization parameter is consistent with that in equilibrium (n_et>10^{13} s cm^{-3}) except for a specific region with the highest temperature (kT=13.3^{+1.4}_{-1.1} keV) where n_et=10^{11.6^{+0.6}_{-1.7}} s cm^{-3}. The elapsed time from the plasma heating estimated from the ionization parameter is 0.36-76 Myr at the 90% confidence level. This time scale is quite short but consistent with the traveling time of a shock to pass through that region. We thus interpret that the non-equilibrium ionization plasma in Abell 754 observed is a remnant of the shock heating in the merger process. We, however, note that the X-ray spectrum of the specific region where the non-equilibrium is found can also be fitted with a collisional ionization plasma model with two temperatures, low kT=4.2^{+4.2}_{-1.5} keV and very high kT > 19.3 keV. The very high temperature component is alternatively fitted with a power law model. Either of these spectral models is interpreted as a consequence of the ongoing merger process as in the case of that with the non-equilibrium ionization plasma.

Discovery of a keV-X-ray excess in RX J1856.5–3754

RX J1856.5

Discovery of an overlapping cluster in the Abell 1674 field with Suzaku

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Soft x-ray transmission of contamination blocking filter for SXI onboard ASTRO-H

3754 is the brightest and nearest (

Simulating Cherenkov Telescope Array observation of RX J1713.7–3946

\sim 120

Performance of front-end mixed-signal ASIC for onboard CCD cameras

pc) source among thermally emitting isolated neutron stars. Its spectra observed with {\sl XMM-Newton} and {\sl Chandra} satellites are well-fitted with the two-temperature (

In-orbit performance of the soft X-ray imaging system aboard Hitomi (ASTRO-H)

kT^\infty \sim

Modeling the spectral response for the soft X-ray imager onboard the ASTRO-H satellite

32 and 63 eV) blackbody model. Fitting ten sets of the data from {\sl Suzaku} XIS0, XIS1, XIS3 and {\sl XMM-Newton} EPIC-pn with the two-temperature blackbody model, we discover an excess emission, 16--26\% in 0.8--1.2\,keV. We examine possible causes of this keV-X-ray excess; uncertainty in the background, pile up of the low energy photons and confusion of other sources. None of them succeeds in explaining the keV-X-ray excess observed with different instruments. We thus consider this keV-X-ray excess is most likely originated in RX J1856.5

Soft X-ray Imager aboard Hitomi (ASTRO-H)

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The Soft X-ray Imager (SXI) aboard Hitomi (ASTRO-H)

3754. However, it is difficult to constrain the spectral shape of the keV-X-ray excess. The third blackbody component with