We investigate long-term X-ray behaviors from the Sgr B2 complex using archival data of the X-ray satellites Suzaku, XMM-Newton, Chandra and ASCA. The observed region of the Sgr B2 complex includes two prominent spots in the Fe I K-$alpha$ line at 6.
40 keV, a giant molecular cloud M 0.66$-$0.02 known as the ``Sgr B2 cloud and an unusual X-ray source G 0.570$-$0.018. Although these 6.40 keV spots have spatial extensions of a few pc scale, the morphology and flux of the 6.40 keV line has been time variable for 10 years, in contrast to the constant flux of the Fe XXV-K$alpha$ line at 6.67 keV in the Galactic diffuse X-ray emission. This time variation is mostly due to M 0.66$-$0.02; the 6.40 keV line flux declined in 2001 and decreased to 60% in the time span 1994--2005. The other spot G 0.570$-$0.018 is found to be conspicuous only in the Chandra observation in 2000. From the long-term time variability ($sim$10 years) of the Sgr B2 complex, we infer that the Galactic Center black hole Sgr A$^*$ was X-ray bright in the past 300 year and exhibited a time variability with a period of a few years.
NeXT (New X-ray Telescope) is the next Japanese X-ray astronomical satellite mission after the Suzaku satellite. NeXT aims to perform wide band imaging spectroscopy. Due to the successful development of a multilayer coated mirror, called a supermirro
r, NeXT can focus X-rays in the energy range from 0.1 keV up to 80 keV. To cover this wide energy range, we are in the process of developing a hybrid X-ray camera, Wideband X-ray Imager (WXI) as a focal plane detector of the supermirror. The WXI consists of X-ray CCDs (SXI) and CdTe pixelized detectors (HXI), which cover the lower and higher X-ray energy bands of 0.1-80 keV, respectively. The X-ray CCDs of the SXI are stacked above the CdTe pixelized detectors of the HXI. The X-ray CCDs of the SXI detect soft X-rays below $sim$ 10 keV and allow hard X-rays pass into the CdTe detectors of the HXI without loss. Thus, we have been developing a back-supportless CCD with a thick depletion layer, a thinned silicon wafer, and a back-supportless structure. In this paper, we report the development and performances of an evaluation model of CCD for the SXI, CCD-NeXT1. We successfully fabricated two types of CCD-NeXT1, unthinned CCDs with 625-um thick wafer and 150-um thick thinned CCDs. By omitting the polishing process when making the thinned CCDs, we confirmed that the polishing process does not impact the X-ray performance. In addition, we did not find significant differences in the X-ray performance between the two types of CCDs. The energy resolution and readout noise are $sim$ 140 eV (FWHM) at 5.9 keV and $sim$5 electrons (RMS), respectively. The estimated thickness of the depletion layer is $sim$80 um. The performances almost satisfy the requirements of the baseline plan of the SXI.
The radio complex Sgr B region is observed with the X-Ray Imaging Spectrometers (XIS) on board Suzaku. This region exhibits diffuse iron lines at 6.4, 6.7 and 6.9 keV, which are K$alpha$ lines of Fe emissiontype{I} (neutral iron), Feemissiontype{XXV}
(He-like iron) and Feemissiontype{XXVI} (H-like iron), respectively. The high energy resolving power of the XIS provides the separate maps of the K-shell transition lines from Feemissiontype{I} (6.4 keV) and Feemissiontype{XXV} (6.7 keV). Although the 6.7 keV line is smoothly distributed over the Sgr B region, a local excess is found near at $(l, b) = (timeform {0D.61}, timeform{0D.01})$, possibly a new SNR. The plasma temperature is textit{kT} $sim$3 keV and the age is estimated to be around several$times10^{3}$ years. The 6.4 keV image is clumpy with local excesses nearby Sgr B2 and at $(l, b) = (timeform{0D.74}, -timeform{0D.09})$. Like Sgr B2, this excess may be another candidate of an X-ray reflection nebula (XRN).
We report the diffuse X-ray emissions from the Sgr A and B regions observed with Suzaku. From the Sgr A region, we found many K-shell transition lines of iron and nickel. The brightest are K alpha lines from FeI, FeXXV and FeXXVI at 6.4 keV, 6.7 keV
and 6.9 keV. In addition, K alpha lines of NiI and NiXXVII, K beta of FeI, FeXXV and FeXXVI, and K gamma of FeXXV and FeXXVI are detected for the first time. The center energy of K alpha of FeXXV favors collisional excitation as the origin for this line emission. The ionization temperature determined from the flux ratio of K alpha of FeXXV and FeXXVI is similar to the electron temperature determined from the flux ratio of K alpha and K beta of FeXXV, which are in the range of 5-7 keV. Consequently, the Galactic Center diffuse X-rays (GCDX) are consistent with emission from a plasma nearly in ionization equilibrium. The radio complex Sgr B region also exhibits K alpha lines of FeI, FeXXV and FeXXVI. The 6.7 keV line (FeXXV) map exhibits a local excess at (l,b) = (0.612, 0.01), and could be a new young SNR. The 6.4 keV image is clumpy with local excesses near Sgr B2 and at (l,b) = (0.74, -0.09). Like Sgr B2, this latter excess may be another X-ray reflection Nebulae (XRN).
We have observed the diffuse X-ray emission from the Galactic center (GC) using the X-ray Imaging Spectrometer (XIS) on Suzaku. The high-energy resolution and the low-background orbit provide excellent spectra of the GC diffuse X-rays (GCDX). The XIS
found many emission lines in the GCDX near the energy of K-shell transitions of iron and nickel. The most pronounced features are FeI K alpha at 6.4 keV and K-shell absorption edge at 7.1 keV, which are from neutral and/or low ionization states of iron, and the K-shell lines at 6.7 keV and 6.9 keV from He-like (FeXXV K alpha) and hydrogenic (FeXXVI Ly alpha) ions of iron. In addition, K alpha lines from neutral or low ionization nickel (NiI K alpha) and He-like nickel (NiXXVII K alpha), and FeI K beta, FeXXV K beta, FeXXVI Ly beta, FeXXV K gamma and FeXXVI Ly gamma are detected for the first time. The line center energies and widths of FeXXV K alpha and FeXXVI Ly alpha favor a collisional excitation (CE) plasma for the origin of the GCDX. The electron temperature determined from the line flux ratio of FeXXV K alpha / FeXXV K beta is similar to the ionization temperature determined from that of FeXXV K alpha /FeXXVI Ly alpha. Thus it would appear that the GCDX plasma is close to ionization equilibrium. The 6.7 keV flux and temperature distribution to the galactic longitude is smooth and monotonic,in contrast to the integrated point source flux distribution. These facts support the hypothesis that the GCDX is truly diffuse emission rather than the integration of the outputs of a large number of unresolved point sources. In addition, our results demonstrate that the chemical composition of Fe in the interstellar gas near the GC is constrained to be about 3.5 times solar.
We present six monitoring observations of the starburst galaxy NGC 2146 using the Chandra X-ray Observatory. We have detected 67 point sources in the 8.7 x 8.7 field of view of the ACIS-S detector. Six of these sources were Ultra-Luminous X-ray Sourc
es, the brightest of which has a luminosity of 5 x 10^{39} ergs s^{-1}. One of the source, with a luminosity of ~1 x 10^{39} ergs s^{-1}, is coincident with the dynamical center location, as derived from the ^{12}CO rotation curve. We suggest that this source may be a low-luminosity active galactic nucleus. We have produced a table where the positions and main characteristics of the Chandra-detected sources are reported. The comparison between the positions of the X-ray sources and those of compact sources detected in NIR or radio does not indicate any definite counterpart. Taking profit of the relatively large number of sources detected, we have derived a logN-logS relation and a luminosity function. The former shows a break at ~10^{-15} ergs cm^{-2} s^{-1}, that we interpret as due to a detection limit. The latter has a slope above the break of 0.71, which is similar to those found in the other starburst galaxies. In addition, a diffuse X-ray emission has been detected in both, soft (0.5--2.0keV) and hard (2.0--10.0keV), energy bands. The spectra of the diffuse component has been fitted with a two (hard and soft) components. The hard power-law component, with a luminosity of ~4 x 10^{39} ergs s^{-1}, is likely originated by unresolved point sources, while the soft component is better described by a thermal plasma model with a temperature of 0.5keV and high abundances for Mg and Si.
