Deconvolution of Images Taken with the Suzaku X-ray Imaging Spectrometer

We present a non-iterative method to deconvolve the spatial response function or the point spread function (PSF) from images taken with the Suzaku X-ray Imaging Spectrometer (XIS). The method is optimized for analyses of extended sources with high photon statistics. Suzaku has four XIS detectors each with its own X-ray CCD and X-Ray Telescope (XRT) and has been providing unique opportunities in spatially-resolved spectroscopic analyses of extended objects. The detectors, however, suffer from broad and position-dependent PSFs with their typical half-power density (HPD) of about 110''. In the authors' view, this shortcoming has been preventing the high collecting area and high spectral resolution of Suzaku to be fully exploited. The present method is intended to recover spatial resolution to ~15'' over a dynamic range around 1:100 in the brightness without assuming any source model. Our deconvolution proceeds in two steps: An XIS image is multiplied with the inverse response matrix calculated from its PSF after rebinning CCD pixels to larger-size tiles (typically 6''x 6''); The inverted image is then adaptively smoothed to obtain the final deconvolved image. The PSF is modeled on a ray-tracing program and an observed point-source image. The deconvolution method has been applied to images of Centaurus A, PSR B1509-58 and RCW 89 taken by one XIS (XIS-1). The results have been compared with images obtained with Chandra to conclude that the spatial resolution has been recovered to ~20'' down to regions where surface brightness is about 1:50 of the brightest tile in the image. We believe the spatial resolution and the dynamic range can be improved in the future with higher fidelity PSF modeling and higher precision pointing information.Comment: 21 pages, accepted for publication in PASJ. A PS file with original-quality figures is available at http://www.slac.stanford.edu/~sugizaki/preprint/pasj3256/sugizaki_No3256.p

THE ASTRO-H MISSION

A review of the Astro-H mission is presented here on behalf of the Astro-H collaboration. 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). One of the main uniquenesses of the ASTRO-H satellite is the high sensitivity and imaging capability of the wide energy band from 0.3 keV to 600 keV. The coverage is achieved by combining the four instruments of the SXS, SXI, HXI, and SGD. The other main uniqueness is a spectroscopic capability not only for a point-like source but also for an extended source with high spectral resolution of ΔE~4÷7eV of SXS. Using the unique powers of these instruments, ASTRO-H will address unresolved issues in high-energy astrophysics

X-ray Measurements of the Particle Acceleration Properties at Inward Shocks in Cassiopeia A

We present new evidence that the bright non-thermal X-ray emission features in the interior of the Cassiopeia A supernova remnant (SNR) are caused by inward moving shocks based on Chandra and NuSTAR observations. Several bright inward-moving filaments were identified using monitoring data taken by Chandra in 2000-2014. These inward-moving shock locations are nearly coincident with hard X-ray (15-40 keV) hot spots seen by NuSTAR. From proper motion measurements, the transverse velocities were estimated to be in the range $\sim$2,100-3,800 km s$^{-1}$ for a distance of 3.4 kpc. The shock velocities in the frame of the expanding ejecta reach values of $\sim$5,100-8,700 km s$^{-1}$, slightly higher than the typical speed of the forward shock. Additionally, we find flux variations (both increasing and decreasing) on timescales of a few years in some of the inward-moving shock filaments. The rapid variability timescales are consistent with an amplified magnetic field of $B \sim$ 0.5-1 mG. The high speed and low photon cut-off energy of the inward-moving shocks are shown to imply a particle diffusion coefficient that departs from the Bohm regime ($k_0 = D_0/D_{\rm 0,Bohm} \sim$ 3-8) for the few simple physical configurations we consider in this study. The maximum electron energy at these shocks is estimated to be $\sim$8-11 TeV, smaller than the values of $\sim$15-34 TeV inferred for the forward shock. Cassiopeia A is dynamically too young for its reverse shock to appear to be moving inward in the observer frame. We propose instead that the inward-moving shocks are a consequence of the forward shock encountering a density jump of $\gtrsim$ 5-8 in the surrounding material.Comment: 16 pages, 8 figures, accepted for publication in Ap

Discovery of a Slow X-Ray Pulsator, AX J1740.1-2847, in the Galactic Center Region

We report the discovery of an X-ray pulsar AX J1740.1-2847 from the Galactic center region. This source was found as a faint hard X-ray object on 7--8 September 1998 with the ASCA Galactic center survey observation. Then, coherent pulsations of P=729 +/- 14 sec period were detected. The X-ray spectrum is described by a flat power-law of ~= 0.7 photon index. The large absorption column of log NH ~= 22.4 (cm^-2) indicates that AX J1740.1-2847 is a distant source, larger than 2.4 kpc, and possibly near at the Galactic center region. The luminosity in the 2--10 keV band is larger than 2.5 x 10^33 erg/s, or likely to be 3.2 x 10^34 erg/s at the Galactic center distance. Although the slow pulse period does not discriminate whether AX J1740.1-2847 is a white dwarf or neutron star binary, the flat power-law and moderate luminosity strongly favor a neutron star binary.Comment: To appear in PASJ Dec. 25, 2000 issue, Vol.52 No.6; 5 pages LaTeX files, uses PASJ95.sty, PASJadd.sty, psfig.sty; also available at http://www-maxi.tksc.nasda.go.jp/%7Esakano/work/paper/index-e.htm

Coronal X-ray emission from an intermediate-age brown dwarf

We report the X-ray detection of the brown dwarf (BD) companion TWA 5B in a $\simeq 12$ Myr old pre-main sequence binary system. We clearly resolve the faint companion (35 photons) separated from the X-ray luminous primary by 2 arcsec in a {\it Chandra} ACIS image. TWA 5B shows a soft X-ray spectrum with a low plasma temperature of only 0.3 keV and a constant flux during the 3 hour observation, of which the characteristics are commonly seen in the solar corona. The X-ray luminosity is 4$\times10^{27}$ erg s$^{-1}$ (0.1--10 keV band) or $\log L_X/L_{bol} = -3.4$. Comparing these properties to both younger and older BDs, we discuss the evolution of the X-ray emission in BDs. During their first few Myr, they exhibit high levels of X-ray activity as seen in higher mass pre-main sequence stars. The level in TWA 5B is still high at $t \simeq 12$ Myr in $\log L_X/L_{bol}$ while $kT$ has already substantially cooled

Chandra Observations of Diffuse X-Rays from the Sagittarius B2 Cloud

We present the first Chandra results of the giant molecular cloud Sagittarius B2 (Sgr B2), located about 100 pc away from the Galactic center. Diffuse X-rays are clearly separated from one-and-a-half dozen resolved point sources. The X-ray spectrum exhibits pronounced iron K-shell transition lines at 6.40 keV (K alpha) and 7.06 keV (K beta), deep iron K-edge at 7.11 keV and large photo-electric absorption at low energy. The absorption-corrected X-ray luminosity is \sim 1 times 10^{35} erg s^{-1}, two orders of magnitude larger than the integrated luminosity of all the resolved point sources. The diffuse X-rays come mainly from the south-west half of the cloud with a concave-shape pointing to the Galactic center direction. These results strongly support the ASCA model that Sgr B2 is irradiated by an X-ray source at the Galactic center side.Comment: 11 pages, 3 figures, to be published in Ap