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The temperatures of the plasma in the supernova remnants (SNRs) are initially very low just after the shock heating. The electron temperature (kT_{e}) increases quickly by Coulomb interaction, and then the energetic electrons gradually ionize atoms to increase the ionization temperature (kT_{i}). The observational fact is that most of the young and middle-to-old aged SNRs have lower kT_{i} than kT_{e} after the shock heating. The temperature evolution in the shell-like SNRs has been explained by this ionizing plasma (IP) scenario. On the other hand, in the last decade, a significant fraction of the mixed morphology SNRs was found to exhibit a recombining plasma (RP) with higher kT_{i} than kT_{e}. The origin and the evolution mechanism of the RP SNRs have been puzzling. To address this puzzle, this paper presents the kT_{e} and kT_{i} profiles using the observed results by follow-up Suzaku observations, and then proposes a new scenario for the temperature and morphology evolutions in the IP and RP SNRs., Accepted for publication in PASJ

This paper reports that the X-ray spectrum from the Galactic Center X-ray Emission (GCXE) is expressed by the assembly of active binaries, non-magnetic Cataclysmic Variables, magnetic Cataclysmic Variables (X-ray active star: XAS), cold matter and diffuse sources. In the fitting of the limited components of the XASs, the GCXE spectrum exhibits significant excesses with $\chi^2/d.o.f. =5.67$. The excesses are found at the energies of K$\alpha$, He$\alpha$, Ly$\alpha$ and radiative recombination continuum of S, Fe and Ni. By adding components of the cold matter and the diffuse sources, the GCXE spectrum is nicely reproduced with $\chi^2/d.o.f. = 1.53$, which is a first quantitative model for the origin of the GCXE spectrum. The drastic improvement is mainly due to the recombining plasmas in the diffuse sources, which indicate the presence of high-energy activity of Sgr A$^*$ in the past of $> 1000$~years., Comment: 7 pages, 3 figures, accepted to PASJ. Unit of EW6.4 in tables 3 and 4 were modified

We report the discovery of an annular emission of $\sim$3'-9' radius around the center of a transient source, an X-ray burster MAXI J1421-613, in the Suzaku follow-up analysis. The spectrum of the annular emission shows no significant emission-line structure, and is well explained by an absorbed power law model with a photon index of $\sim$4.2. These features exclude the possibility that the annular emission is a shell-like component of a supernova remnant. The spectral shape, the time history, and the X-ray flux of the annular emission agree with the scenario that the emission is due to a dust-scattering echo. The annular emission is made under a rare condition of the dust-scattering echo, where the central X-ray source, MAXI J1421-613, exhibits a short time outburst with three X-ray bursts and immediately re-enters a long quiescent period. The distribution of the hydrogen column density along the annular emission follows that of the CO intensity, which means that MAXI J1421-613 is located behind the CO cloud. We estimate the distance to MAXI J1421-613 to be $\sim$3~kpc assuming that the dust layer responsible for the annular emission is located at the same position as the CO cloud., Comment: 11 pages, 3 figures, accepted for publication in Publications of the Astronomical Society of Japan (PASJ)

This paper reports the analysis procedure and results of simultaneous spectral fits of the Suzaku archive data for Sagittarius (Sgr) A East and the nearby Galactic center X-ray emission (GCXE). The results are that the mixed-morphology supernova remnant Sgr A East has a recombining plasma (RP) with Cr and Mn He$\alpha$ lines, and a power-law component (PL) with an Fe I K$\alpha$ line. The nearby GCXE has a $\sim$1.5-times larger surface brightness than the mean GCXE far from Sgr A East, although the spectral shape is almost identical. Based on these results, we interpret that the origins of the RP and the PL with the Fe I K$\alpha$ line are past big flares of Sgr A$^*$., Comment: Accepted for publication in PASJ

We report a discovery of bright blob-like enhancements of an Fe I K$\alpha$ line in the northwest and the middle of the supernova remnant (SNR) IC 443. The distribution of the line emission is associated with molecular clouds interacting with the shock front, and is totally different from that of the plasma. The Fe I K$\alpha$ line has a large equivalent width. The most plausible scenario for the origin of the line emission is that the MeV protons accelerated in the shell leak into the molecular clouds and ionize the Fe atoms therein. The observed Fe I K$\alpha$ line intensity is consistent with the prediction of a theoretical model, in which MeV protons are accelerated along with GeV and TeV protons at the SNR., Comment: 13 pages, 3 figures, accepted for publication in PASJ

Most of young and middle-aged supernova remnants (SNRs) exhibit an ionizing plasma (IP), an ionizing process following a shock heated SNR gas. On the other hand, significant fractions of SNRs exhibit a recombining plasma (RP). The origin and the mechanisms of the RP, however, are not yet well understood. This paper proposes a new model that the RP is followed after the IP process taken at the first epoch of the SNR evolution. Using the high quality and wide band (0.6-10 keV) spectrum of IC 443, we nicely fitted with a model of two RP (two-RP model) plus a power law (PL) with an Fe I Kalpha line component. The ionization temperature in one RP monotonously increases from Ne-Ca, while that in the other RP shows a drastic increase from Cr-Ni. Origin and mechanism of the two-RP and PL with an Fe I Kalpha line components are possibly due to a different evolution of two plasmas and ionization by the low-energy cosmic ray., Accepted for publication in PASJ

著者人数: 193名(所属. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS): 堂谷, 忠靖; 海老沢, 研; 林, 克洋; 飯塚, 亮; 井上, 芳幸; 石田, 学; 石川, 久美; 岩井, 将親; 国分, 紀秀; 小山, 志勇; 前田, 良知; 満田, 和久; 中川, 貴雄; 尾崎, 正伸; 佐藤, 悟郎; 佐藤, 理江; Simionescu, Aurora; 菅原, 泰晴; 高橋, 忠幸; 竹井, 洋; 田村, 隆幸; 田中, 靖郎; 冨田, 洋; 辻本, 匡弘; 上田, 周太朗; 渡辺, 伸; 山崎, 典子; 内田, 悠介), Accepted: 2018-09-30, 資料番号: SA1180351000

著者人数: Hitomi Collaboration 193名（所属. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS): 堂谷, 忠靖; 海老沢, 研; 萩野, 浩一; 林, 克洋; 飯塚, 亮; 井上, 芳幸; 石田, 学; 石川, 久美; 岩井, 将親; 国分, 紀秀; 小山, 志勇; Lee, Shiu-Hang; 前田, 良知; 満田, 和久; 中川, 貴雄; 尾崎, 正伸; 佐藤, 悟郎; 佐藤, 理江; Simionescu, Aurora; 菅原, 泰晴; 高橋, 忠幸; 竹井, 洋; 田村, 隆幸; 田中, 靖郎; 冨田, 洋; 辻本, 匡弘; 上田, 周太朗; 渡辺, 伸; 山崎, 典子）, Number of authors: Hitomi Collaboration 193 (Affiliation. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS): Dotani, Tadayasu; Ebisawa, Ken; Hagino, Kouichi; Hayashi, Katsuhiro; Iizuka, Ryo; Inoue, Yoshiyuki; Ishida, Manabu; Ishikawa, Kumi; Iwai, Masachika; Kokubun, Motohide; Koyama, Shu; Lee, Shiu-Hang; Maeda, Yoshitomo; Mitsuda, Kazuhisa; Nakagawa, Takao; Ozaki, Masanobu; Sato, Goro; Sato, Rie; Simionescu, Aurora; Sugawara, Yasuharu; Takahashi, Tadayuki; Takei, Yoh; Tamura, Takayuki; Tanaka, Yasuo; Tomida, Hiroshi; Tsujimoto, Masahiro; Ueda, Shutaro; Watanabe, Shin; Yamasaki, Noriko Y.), Accepted: 2017-11-16, 資料番号: SA1170338000

著者人数: Hitomi Collaboration 193名（所属. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS): 堂谷, 忠靖; 海老沢, 研; 萩野, 浩一; 林, 克洋; 飯塚, 亮; 井上, 芳幸; 石田, 学; 石川, 久美; 岩井, 将親; 国分, 紀秀; 小山, 志勇; 前田, 良知; 満田, 和久; 中川, 貴雄; 尾崎, 正伸; 佐藤, 悟郎; 佐藤, 理江; Simionescu, Aurora; 菅原, 泰晴; 高橋, 忠幸; 竹井, 洋; 田村, 隆幸; 冨田, 洋; 辻本, 匡弘; 上田, 周太朗; 渡辺, 伸; 山崎, 典子; 中庭, 望）, Number of authors: Hitomi Collaboration 193 (Affiliation. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS): Dotani, Tadayasu; Ebisawa, Ken; Hagino, Kouichi; Hayashi, Katsuhiro; Iizuka, Ryo; Inoue, Yoshiyuki; Ishida, Manabu; Ishikawa, Kumi; Iwai, Masachika; Kokubun, Motohide; Koyama, Shu; Maeda, Yoshitomo; Mitsuda, Kazuhisa; Nakagawa, Takao; Ozaki, Masanobu; Sato, Goro; Sato, Rie; Simionescu, Aurora; Sugawara, Yasuharu; Takahashi, Tadayuki; Takei, Yoh; Tamura, Takayuki; Tomida, Hiroshi; Tsujimoto, Masahiro; Ueda, Shutaro; Watanabe, Shin; Yamasaki, Noriko Y.), Masahiro; Ueda, Shutaro; Watanabe, Shin; Yamasaki, Noriko Y.; Nakaniwa, Nozomi), Accepted: 2017-11-02, 資料番号: SA1170342000

著者人数: 196名(所属. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS): 堂谷, 忠靖; 海老沢, 研; 林, 克洋; 飯塚, 亮; 井上, 芳幸; 石田, 学; 石川, 久美; 岩井, 将親; 国分, 紀秀; 小山, 志勇; 前田, 良知; 満田, 和久; 中川, 貴雄; 尾崎, 正伸; 佐藤, 悟郎; 佐藤, 理江; Simionescu, Aurora; 菅原, 泰晴; 高橋, 忠幸; 竹井, 洋; 田村, 隆幸; 田中, 靖郎; 冨田, 洋; 辻本, 匡弘; 上田, 周太朗; 渡辺, 伸; 山崎, 典子; 佐藤, 寿紀; 中庭, 望), Number of authors: Hitomi Collaboration 197 (Affiliation. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS): Dotani, Tadayasu; Ebisawa, Ken; Hayashi, Katsuhiro; Hayashi, Tasuku; Iizuka, Ryo; Inoue, Yoshiyuki; Ishida, Manabu; Ishikawa, Kumi; Iwai, Masachika; Kokubun, Motohide; Koyama, Shu; Maeda, Yoshitomo; Mitsuda, Kazuhisa; Nakagawa, Takao; Ozaki, Masanobu; Sato, Goro; Sato, Rie; Simionescu, Aurora; Sugawara, Yasuharu; Takahashi, Tadayuki; Takei, Yoh; Tamura, Takayuki; Tanaka, Yasuo; Tomida, Hiroshi; Tsujimoto, Masahiro; Ueda, Shutaro; Watanabe, Shin; Yamasaki, Noriko Y.; Sato, Toshiki; Nakaniwa, Nozomu), Accepted: 2018-02-14, 資料番号: SA1180104000

The Galactic Center X-ray Emission (GCXE) is composed of high temperature (7 keV) and low temperature (1 keV) plasmas (HTP and LTP, respectively). The global structure of the HTP is roughly uniform over the Galactic center (GC) region, and the origin of the HTP has been extensively studied. On the other hand, the LTP is more clumpy, and the origin has not been studied in detail. In the S XV He alpha line map, a pair of horn-like soft diffuse sources are seen at the symmetric positions with respect to Sagittarius A^{star}. The X-ray spectra of the pair are well represented by an absorbed thin thermal plasma model of a temperature and N_H of 0.6-0.7 keV and 4x10^{22} cm^{-2}, respectively. The N_H values indicate that the pair are located near at the GC. Then the dynamical time scales of the pair are 10^{5} yr. The Si and S abundances and the surface brightnesses in the S XV He alpha line band are 0.7-1.2 and 0.6-1.3 solar, and (2.0-2.4)x10^{-15} erg s^{-1} cm^{-2} arcmin^{-2}, respectively. The temperature, abundances, and surface brightness are similar to those of the LTP in the GCXE, while the abundances are far larger than those of known point sources, typically coronal active stars and RS CVn-type active binaries. Based on these results, possible origin of the LTP is discussed., Comment: Accepted for publication in PASJ

HESS J1841$-$055 is a diffuse unidentified gamma-ray source with the size of $\sim\,1.3^{\circ}\times\,1^{\circ}$. No conclusive counterpart in other wavelengths has so far detected. To search for X-rays responsible for the TeV emission, the Suzaku observations were conducted, which covered a half region of the HESS source. In the soft band (0.5-2.0 keV), we discovered a diffuse emission, Suzaku J1840.2$-$0552, with the size of $\sim10'$. Since its spectrum was fitted by an optically thin thermal plasma model, Suzaku J1840.2$-$0552 is likely to be a supernova remnant. We also discovered an extended source, Suzaku J1840.2$-$0544, in the hard band (2.0-8.0 keV) with an emission line at 6.1 keV. From the spectral feature and large interstellar absorption, this source is likely to be a cluster of galaxies behind the Galactic plane at the red-shift of $\sim$0.09. The other diffuse source spatially overlaps with the SNR candidate G26.6$-$0.2, which shows a non-thermal dominant spectrum. Since no other candidate is found in the hard X-ray band, we infer that these largely extended sources could be possible counterparts of HESS J1841$-$055., 17 pages, 5 figures

著者人数: Hitomi Collaboration 193名 (所属. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS): 堂谷, 忠靖; 海老沢, 研; 林, 克洋; 飯塚, 亮; 井上, 芳幸; 石田, 学; 石川, 久美; 岩井, 將親; 国分, 紀秀; 小山, 志勇; 前田, 良知; 満田, 和久; 中川, 貴雄; 尾崎, 正伸; 佐藤, 悟郎; 佐藤, 理江; Simionescu, Aurora; 菅原, 泰晴; 高橋, 忠幸; 竹井, 洋; 田村, 隆幸; 田中, 靖郎; 冨田, 洋; 辻本, 匡弘; 上田, 周太朗; 渡辺, 伸; 山崎, 典子), Number of authors: Hitomi Collaboration 193 (Affiliation. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS): Dotani, Tadayasu; Ebisawa, Ken; Hayashi, Katsuhiro; Iizuka, Ryo; Inoue, Yoshiyuki; Ishida. Manabu; Ishikawa, Kumi; Iwai, Masachika; Kokubun, Motohide; Koyama, Shu; Maeda, Yoshitomo; Mitsuda, Kazuhisa; Nakagawa, Takao; Ozaki, Masanobu; Sato, Goro; Sato, Rie; Simionescu, Aurora; Sugawara, Yasuharu; Takahashi, Tadayuki; Takei, Yoh; Tamura, Takayuki; Tanaka, Yasuo; Tomida, Hiroshi; Tsujimoto, Masahiro; Ueda, Shutaro; Watanabe, Shin; Yamasaki, Noriko Y.), Accepted: 2017-09-21, 資料番号: SA1170128000

Cosmic rays (CRs) in our galaxy are thought to be generated via diffusive shock acceleration. Gamma-ray observations have revealed that protons and/or electrons are accelerated to energies up to 100 TeV in supernova remnants (SNRs), and hence SNRs are the most plausible source of CR production. Whereas low-energy cosmic rays (LECRs) below the MeV band have important information on the initial acceleration mechanism, there has been very little information on LECRs due to lack of an effective probe. Interacting with neutral iron atoms in the interstellar medium, LECRs produce fluorescent X-ray line emission at 6.40 keV. The 6.40 keV line observation can be a unique probe to investigate LECRs. Analyzing the Suzaku data, we discovered the 6.40 keV line emission from several SNRs interacting with molecular clouds (W28, W44, Kes 67, Kes 69, Kes 78, Kes 79, and 3C391). The 6.40 keV line emission would be produced by MeV protons with the energy density of $>10$ eV cm$^{-3}$. Furthermore, we discovered the 6.40 keV line emission from a giant molecular cloud located near the Galactic center. The energy density of MeV protons is estimated to be 80 eV cm$^{-3}$. The diffusion length of MeV protons is only a few tens of parsecs, and thus the MeV protons should be produced in situ. Surprisingly, there is no SNR in the vicinity. The LECRs would possibly be generated by stochastic acceleration via Alfven turbulence.

We observed the Galactic mixed-morphology supernova remnant G166.0+4.3 with Suzaku. The X-ray spectrum in the western part of the remnant is well represented by a one-component ionizing plasma model. The spectrum in the northeastern region can be explained by two components. One is the Fe-rich component with the electron temperature $kT_e = 0.87_{-0.03}^{+0.02}$ keV. The other is the recombining plasma component of lighter elements with $kT_e = 0.46\pm0.03$ keV, the initial temperature $kT_{init} = 3$ keV (fixed) and the ionization parameter $n_et = (6.1_{-0.4}^{+0.5}) \times 10^{11} \rm cm^{-3} s$. As the formation process of the recombining plasma, two scenarios, the rarefaction and thermal conduction, are considered. The former would not be favored since we found the recombining plasma only in the northeastern region whereas the latter would explain the origin of the RP. In the latter scenario, an RP is anticipated in a part of the remnant where blast waves are in contact with cool dense gas. The emission measure suggests higher ambient gas density in the northeastern region. The morphology of the radio shell and a GeV gamma-ray emission also suggest a molecular cloud in the region., 8 pages, 7 figures, accepted for publication in PASJ

We present the discovery of out-flow like plasma emissions with the Suzaku and ASCA data. Those plasmas have a size of ∼150 pc. Remarkably, the southern plasma is in a recombination dominant phase, which is not predicted by standard shock heating. A plausible scenario is either photoionization due to strong jet-like X-rays from Sgr A* or rapid cooling due to adiabatic expansion of a blowout plasma from the Galactic center about 105 years ago.

This paper reports the analysis of the X-ray spectra of the Galactic diffuse X-ray emission (GDXE) in the Suzaku archive. The fluxes of the Fe I K alpha (6.4 keV), Fe XXV,He alpha (6.7 keV) and Fe XXVI Ly alpha (6.97 keV) lines are separately determined. From the latitude distributions, we confirm that the GDXE is decomposed into the Galactic center (GCXE), the Galactic bulge (GBXE) and the Galactic ridge (GRXE) X-ray emissions. The scale heights (SHs) of the Fe XXV He alpha line of the GCXE, GBXE and GRXE are determined to be ~40, ~310 and ~140 pc, while those of the Fe I K alpha line are ~30, ~160 and ~70 pc, respectively. The mean equivalent widths (EWs) of the sum of the Fe XXV He alpha and Fe XXVI Ly alpha lines are ~750 eV, ~600 eV and ~550 eV, while those of the Fe I K alpha line are ~150~eV, ~60~eV and ~100~eV for the GCXE, GBXE and GRXE, respectively. The origin of the GBXE, GRXE and GCXE is separately discussed based on the new results of the SHs and EWs, in comparison with those of the Cataclysmic Variables (CVs), Active Binaries (ABs) and Coronal Active stars (CAs)., Comment: Accepted for publication in PASJ

We have surveyed spatial profiles of the Fe K$\alpha$ lines in the Galactic center diffuse X-rays (GCDX), including the transient region from the GCDX to the Galactic ridge X-ray emission (GRXE), with the Suzaku satellite. We resolved Fe K$\alpha$ line complex into three lines of Fe \emissiontype{I}, Fe \emissiontype{XXV} and Fe \emissiontype{XXVI} K$\alpha$, and obtained their spatial intensity profiles with the resolution of $\sim \timeform{0D.1}$. We compared the Fe \emissiontype{XXV} K$\alpha$ profile with a stellar mass distribution (SMD) model made from near infrared observations. The intensity profile of Fe \emissiontype{XXV} K$\alpha$ is nicely fitted with the SMD model in the GRXE region, while that in the GCDX region shows $3.8\pm0.3$ $(\timeform{0D.2}, Comment: Accepted by PASJ

Supernova remnants (SNRs) are the primary candidate of Galactic cosmic-ray accelerators. It is still an open issue when and how young SNRs, which typically exhibit strong synchrotron X-rays and GeV and TeV gamma-rays, undergo the state transition to middle-aged SNRs dominated by thermal X-rays and GeV gamma-rays. The SNR N132D in the Large Magellanic Cloud is an ideal target to study such a transition, exhibiting bright X-rays and gamma-rays, and with the expected age of ~2500 yrs. In this paper we present results of NuSTAR and Suzaku spectroscopy. We reveal that N132D has a nearly equilibrium plasma with a temperature of > 5 keV or a recombining plasma with a lower temperature (~1.5 keV) and a recombining timescale (net) of 8.8 (7.0--10.0)e12 cm^-3s. Together with the center filled morphology observed in the iron K line image, our results suggest that N132D is now at transition stage from a young SNR to middle-aged. We have constrained the tight upper-limit of nonthermal X-rays. Bright gamma-rays compared to faint nonthermal X-rays suggest that the gamma-rays are hadronic in origin. The spectral energy distribution from radio to gamma-rays shows a proton cut-off energy of ~30 TeV. These facts confirm that N132D is in the transition from young to middle-aged SNR. The large thermal energy of > 10^51 erg and accelerated proton energy of ~ 10^50 erg suggest the supernova explosion might have been very energetic., 11 pages, 13 figures, ApJ, in press

A 20' \times 16' elliptical ring-like structure has been found near the Galactic center in the narrow energy band corresponding to the K$\alpha$ line from He-like sulfur. In the ring, two diffuse sources are found, a supernova remnant candidate G359.79-0.26 and an unidentified source G359.77-0.09. The X-ray spectrum of G359.77-0.09 is similar to that of G359.79-0.26, which can be explained by an absorbed thin thermal plasma model with temperatures of 0.7 and 1.0 keV. The absorption column densities of these two sources are large (N_H = 6.9 \times 10^{22} and 4.5 \times 10^{22} cm^{-2}) and are consistent with that of the Galactic center distance. The X-ray spectrum extracted from the ring-like structure is also represented by an absorbed thin thermal plasma model (kT_e \sim 0.9 keV). The thermal energy of the plasma filling the ring-like structure is estimated to be 1.0 \times 10^{51} erg. We therefore propose that the two sources comprise a single ring-like object, which is possibly a super bubble with a size of 49 pc \times 40 pc in the Galactic center region., Comment: 9 pages, 7 figures, accepted for publication in PASJ

We report results of the Suzaku observation toward the Sagittarius (Sgr) D region. Diffuse X-ray emission was clearly detected from inside the shell-type supernova remnant, the Sgr D SNR and is named G 1.02-0.18. A hint of an iron line is seen in the spectrum, suggesting that G 1.02-0.18 is a thin thermal plasma with the temperature of kT ∼ 2 keV . Its physical parameters (e.g. the plasma density, mass, thermal energy) suggest that G 1.02-0.18 is an SNR candidate and is possibly associated with the Sgr D SNR. We also analyzed data from another bright X-ray source SAX J1748.2-2808, which was in the field of view of Suzaku. A coherent pulsation with a period of 593 s and emission lines from neutral and highly ionized irons were discovered. These results indicate that SAX J1748.2-2808 is likely to be an intermediate polar.

We present the Suzaku results on a new candidate of a supernova remnant (SNR) in the Sagittarius C region. We detected diffuse X-rays of an elliptical shape (G359.41-0.12) and a chimney-like structure (the Chimney), both of which were fitted with a thin thermal the model of kBT ~1 keV temperature. The absorption columns are same between these two structures, indicating that both are located at the same distance in the same line of sight. The narrow band image and one-dimensional profile of S XV Kalpha at 2.45 keV show that the Chimney is emanating from G359.41-0.12. Therefore, these two sources are physically connected with each other. The sum of the thermal energies of the Chimney and G359.41-0.12 is estimated to be 1.4x10^50 erg, typical for a galactic SNR. G359.41-0.12 is likely to be a new SNR candidate and the Chimney is an associated outflow., 10 pages, 4 figures

This paper reports on the first results of the Suzaku observation in the Sgr C region. We detected four diffuse clumps with strong line emission at 6.4keV, Ka from neutral or low-ionized Fe. One of them, M359.38-0.00, is newly discovered with Suzaku. The X-ray spectra of the two bright clumps, M359.43-0.07 and M359.47-0.15, after subtracting the Galactic center diffuse X-ray emission (GCDX), exhibit strong Ka line from FeI with large equivalent widths (EWs) of 2.0-2.2keV and clear Kb of FeI. The GCDX in the Sgr C region is composed of the 6.4keV- and 6.7keV-associated components. These are phenomenologically decomposed by taking relations between EWs of the 6.4keV and 6.7keV lines. Then the former EWs against the associated continuum in the bright clump regions are estimated to be 2.4(+2.3_-0.7)keV. Since the two different approaches give similar large EWs of 2keV, we strongly suggest that the 6.4keV clumps in the Sgr C region are due to X-ray reflection/fluorescence (the X-ray reflection nebulae).

We made a 100 ks observation of the Sagittarius (Sgr) B1 region at (l, b) = (0.5, -0.1) near to the Galactic center (GC) with the Suzaku/XIS. Emission lines of S XV, Fe I, Fe XXV, and Fe XXVI were clearly detected in the spectrum. We found that the Fe XXV and Fe XXVI line emissions smoothly distribute over the Sgr B1 and B2 regions connecting from the GC. This result suggests that the GC hot plasma extends at least up to the Sgr B region with a constant temperature. There are two diffuse X-ray sources in the observed region. One of the two (G0.42-0.04) is newly discovered, and exhibits a strong S XV Ka emission line, suggesting a candidate for a supernova remnant located in the GC region. The other one (M0.51-0.10), having a prominent Fe I Ka emission line and a strongly absorbed continuum, is likely to be an X-ray reflection nebula. There is no near source bright enough to irradiate M0.51-0.10. However, the Fe I Ka emission can be explained if Sgr A* was ~ 10^6 times brighter 300 years ago, the light travel time for 100 pc to M0.51-0.10, than it is at present., 10 pages, 10 figures

We report on the diffuse X-ray emission from the Galactic Centre (GCDX) observed with the X-ray Imaging Spectrometer (XIS) on board the Suzaku satellite. The highly accurate energy calibration and extremely low background of the XIS provide many new facts on the GCDX. These are (1) the origin of the lines at 6.7 and 7.0 keV is collisional excitation in a hot plasma, (2) the discovery of new SNR and super-bubble candidates, (3) most of the 6.4 keV line is X-ray fluorescence, and (4) time variability of the 6.4 keV line is found from the Sgr B2 complex. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on the diffuse X-ray emissions from the Galactic center (GCDX) observed with the X-ray Imaging Spectrometer (XIS) on board the Suzaku satellite. The highly accurate energy calibrations and extremely low background of the XIS provide many new facts on the GCDX. These are (1) the origin of the 6.7/7.0keV lines is collisional excitation in hot plasma, (2) new SNR and super-bubble candidates are found, (3) most of the 6.4keV line is fluorescence by X-rays, and (4) time variability of the 6.4keV line is found from the SgrB2 complex., Comment: 4 pages, 6 figure, proceedings of the XMM-Newton workshop, June 2007, accepted for publication in AN

An elongated X-ray source with a strong K-shell line from He-like iron (Fe XXVI) is found at (RA, Dec)_{J2000.0}=(17h44m00s.0, -29D13'40''.9) in the Galactic center region. The position coincides with the X-ray thread, G359.55+0.16, which is aligned with the radio non-thermal filament. The X-ray spectrum is well fitted with an absorbed thin thermal plasma (apec) model. The best-fit temperature, metal abundance, and column density are 4.1^{+2.7}_{-1.8} keV, 0.58^{+0.41}_{-0.32} solar, and 6.1^{+2.5}_{-1.3}x10^{22} cm^{-2}, respectively. These values are similar to those of the largely extended Galactic center X-ray emission., Accepted for publication in PASJ

We present Suzaku results of the two Galactic supernova remnants (SNRs), G350.1-0.3 and G349.7+0.2. We find Al and Ni K alpha lines from both the SNRs for the first time, in addition to previously detected K-shell lines of Mg, Si, S, Ar, Ca and Fe. The spectra are well described by two optically thin thermal plasmas: a low-temperature (low-kT) plasma in collisional ionization equilibrium and a high-temperature (high-kT) plasma in non-equilibrium ionization. Since the low-kT plasma has solar metal abundances, it is thought to be of interstellar medium origin. The high-kT plasma has super-solar abundances, hence it is likely to be of ejecta origin. The abundance patterns of the ejecta components are similar to those of core-collapse supernovae with the progenitor mass of ~15-25 M_solar for G350.1-0.3 and ~35-40 M_solar for G349.7+0.2. We find extremely high abundances of Ni compared to Fe (Z_Ni/Z_Fe ~8). Based on the measured column densities between the SNRs and the near sky background, we propose that G350.1-0.3 and G349.7+0.2 are located at the distance of 9+/-3 kpc and 12+/-5 kpc, respectively. Then the ejecta masses are estimated to be ~13 M_solar and ~24 M_solar for G350.1-0.3 and G349.7+0.2, respectively. These values are consistent with the progenitor mass of ~15-25 M_solar and ~35-40 M_solar for G350.1-0.3 and G349.7+0.2, respectively., 9 pages, 6 figures, accepted for publication in PASJ

This paper reports detailed K-shell line profiles of iron (Fe) and nickel (Ni) of the Galactic Center X-ray Emission (GCXE), Galactic Bulge X-ray Emission (GBXE), Galactic Ridge X-ray Emission (GRXE), magnetic Cataclysmic Variables (mCVs), non-magnetic Cataclysmic Variables (non-mCVs), and coronally Active Binaries (ABs). For the study of the origin of the GCXE, GBXE, and GRXE, the spectral analysis is focused on equivalent widths of the Fe K$\alpha$, Fe He$\alpha$, and Fe Ly$\alpha$ lines. The global spectrum of the GBXE is reproduced by a combination of the mCVs, non-mCVs, and ABs spectra. On the other hand, the GRXE spectrum shows significant data excesses at the Fe K$\alpha$ and Fe He$\alpha$ line energies. This means that additional components other than mCVs, non-mCVs, and ABs are required, which have symbiotic phenomena of cold gas and very high-temperature plasma. The GCXE spectrum shows larger excesses than those found in the GRXE spectrum at all the K-shell lines of iron and nickel. Among them the largest ones are the Fe K$\alpha$, Fe He$\alpha$, Fe Ly$\alpha$, and Fe Ly$\beta$ lines. Together with the fact that the scale heights of the Fe K$\alpha$, Fe He$\alpha$, and Fe Ly$\alpha$ lines are similar to that of the central molecular zone (CMZ), the excess components would be related to high-energy activity in the extreme envelopment of the CMZ., Comment: 12 pages, 10 figures, 5 tables, published in ApJ

We present quantitative investigation on the past activities of Sgr A* from the three dimensional position of multiple X-ray reflection nebulae.

We observed the supergiant fast X-ray transient (SFXT) AX J1841.0-0536 with Suzaku. Many short flares with durations of ~100 s were detected in the XIS and HXD bands. We found that the overall spectrum in the 1.0-40 keV band was fitted with an partially absorbed cut-off power-law plus an Fe I Kα line and an absorption feature at the center energy of ~15 keV, that we interpret as possible evidence of a resonant cyclotron absorption feature. We then made time-resolved spectra and fit them with the same models as the overall spectrum. The photon indices of the power-law were distributed in 0-2 with the trend of "harder when brighter". On the other hand, no significant difference was found, either in the absorption column densities nor in the covering fractions between any of the phases.

We have surveyed the spatial profile of the Fe Kα lines in the Galactic center diffuse X-rays (GCDX), including the transient region from the GCDX to the Galactic ridge X-ray emission (GRXE) using the Suzaku XIS data. We compared Fe XXV Kα profile with a stellar mass distribution (SMD) model made from near infrared observations. The Fe XXV Kα profile is nicely fitted with the SMD model in the GRXE region, while that in the GCDX region shows about 4-19 times excess over the best-fit SMD model in the GRXE region. Thus Fe XXV Kα in the GCDX is hardly explained by the same origin of the GRXE.

We present the Suzaku results of the supernova remnant (SNR) G346.6-0.2. The X-ray emission has a center-filled morphology with the size of 6' x 8' within the radio shell. Neither an ionization equilibrium nor non-equilibrium (ionizing) plasma can reproduce the spectra remaining shoulder-like residuals in the 2-4 keV band. These structures are possibly due to recombination of free electrons to the K-shell of He-like Si and S. The X-ray spectra are well fitted with a plasma model in a recombination dominant phase. We propose that the plasma was in nearly full ionized state at high temperature of 5 keV, then the plasma changed to a recombining phase due to selective cooling of electrons to lower temperature of 0.3 keV. G346.6-0.2 would be in an epoch of the recombining phase., Comment: Accepted for publication in PASJ

There are K-shell emission lines of neutral Fe K (Fe I K) correlated with giant molecular clouds in the Galactic center (GC) region. The Fe I K emission is one of the key for the structure and activity of the GC, including the super-massive black hole Sagittarius A* (hereafter Sgr A*) with a huge mass of four million solar. The origin of the Fe I K is still an open question. In order to resolve the problem, we made deep observations of the GC region with Suzaku. From the high-quality Xray data taken by Suzaku, we have found many clouds emitting the Fe I K line and have revealed the following new facts: (1) emission lines of neutral heavy atoms other than Fe, (2) time variability of the X-ray flux from the molecular clouds, (3) measurement of three-dimensional distribution of the molecular clouds. From these results, we reached a conclusion that Sgr A* made X-ray flares several hundred years ago and illuminated the molecular clouds in the vicinity.

We report the global distribution of the intensities of the K-shell lines from the He-like and H-like ions of S, Ar, Ca and Fe along the Galactic plane. From the profiles, we clearly separate the Galactic center X-ray emission (GCXE) and the Galactic ridge X-ray emission (GRXE). The intensity profiles of the He-like K$\alpha$ lines of S, Ar, Ca and Fe along the Galactic plane are approximately similar with each other, while not for the H-like Ly$\alpha$ lines. In particular, the profiles of H-like Ly$\alpha$ of S and Fe show remarkable contrast; a large excess of Fe and almost no excess of S lines in the GCXE compared to the GRXE. Although the prominent K-shell lines are represented by $\sim$1 keV and $\sim$7 keV temperature plasmas, these two temperatures are not equal between the GCXE and GRXE. In fact, the spectral analysis of the GCXE and GRXE revealed that the $\sim$1 keV plasma in the GCXE has lower temperature than that in the GRXE, and vice versa for the $\sim$7 keV plasma., Comment: Accepted by PASJ. It will be published in PASJ Vol.65 No. 2

The high energy activity in the inner few degrees of the Galactic center is traced by diffuse radio, X-ray and gamma-ray emission. The physical relationship between different components of diffuse gas emitting at multiple wavelengths is a focus of this work. We first present radio continuum observations using Green Bank Telescope and model the nonthermal spectrum in terms of a broken power-law distribution of GeV electrons emitting synchrotron radiation. We show that the emission detected by Fermi is primarily due to nonthermal bremsstrahlung produced by the population of synchrotron emitting electrons in the GeV energy range interacting with neutral gas. The extrapolation of the electron population measured from radio data to low and high energies can also explain the origin of FeI 6.4 keV line and diffuse TeV emission, as observed with Suzaku, XMM-Newton, Chandra and the H.E.S.S. observatories. The inferred physical quantities from modeling multi-wavelength emission in the context of bremsstrahlung emission from the inner 300x120 parsecs of the Galactic center are constrained to have the cosmic ray ionization rate 1-10x10^{-15} s^-1, molecular gas heating rate elevating the gas temperature to 75-200K, fractional ionization of molecular gas 10^{-6} to 10^{-5}, large scale magnetic field 10-20 micro Gauss, the density of diffuse and dense molecular gas 100 and 10^3 cm^{-3} over 300pc and 50pc pathlengths, and the variability of FeI Kalpha 6.4 keV line emission on yearly time scales. Important implications of our study are that GeV electrons emitting in radio can explain the GeV gamma-rays detected by Fermi and that the cosmic ray irradiation model, like the model of the X-ray irradiation triggered by past activity of Sgr A*, can also explain the origin of the variable 6.4 keV emission from Galactic center molecular clouds., Comment: 51 pages, 12 figures, ApJ (in press) minor changes in equations 3, 4, 6, 7

We investigated the emission of K$\alpha$ iron line from the massive molecular clouds in the Galactic center (GC). We assume that at present the total flux of this emission consists of time variable component generated by primary X-ray photons ejected by Sagittarius A$^\ast$ (Sgr A$^\ast$) in the past and a relatively weak quasi-stationary component excited by impact of protons which were generated by star accretion onto the central black hole. The level of background emission was estimated from a rise of the 6.4 keV line intensity in the direction of several molecular clouds, that we interpreted as a stage when the X-ray front ejected by Sgr A$^\ast$ entered into these clouds. The 6.4 keV emission before this intensity jump we interpreted as emission generated by subrelativistic cosmic rays there. The cross-section of K$\alpha$ vacancies produced by protons differs from that of electrons or X-rays. Therefore, we expect that this processes can be distinguished from the analysis of the equivalent width of the iron line and time variations of the width can be predicted. The line intensity from the clouds depends on their distance from Sgr A$^\ast$ and the coefficient of spacial diffusion near the Galactic center. We expect that in a few years the line intensity for the cloud G\,0.11$-$0.11 which is relatively close to Sgr A$^\ast$ will decreases to the level $\lesssim$ 10% from its present value. For the cloud Sagittarius B2 (Sgr B2) the situation is more intricate. If the diffusion coefficient $D\gtrsim 10^{27}$ cm$^2$ s$^{-1}$ then the expected stationary flux should be about 10% of its level in 2000. In the opposite case the line intensity from Sgr B2 should drop down to zero because the protons do not reach the cloud., Comment: PASJ accepted

Prominent K-shell emission lines of neutral iron (hereafter, FeI-K) and hard-continuum X-rays were found from molecular clouds (MCs) in the Sagittarius B (Sgr B) region with the two separate Suzaku observations in 2005 and 2009. The X-ray flux of FeI-K decreased in correlation to the hard-continuum flux by factor of 0.4-0.5 in 4 years, which is nearly equal to the light-travelling across the MCs. The rapid and correlated time-variability, the equivalent width of FeI-K, and the K-edge absorption depth of FeI are consistently explained by "X-ray echoes" due to the fluorescent and Thomson-scattering of an X-ray flare from an external source. The required flux of the X-ray flare depends on the distance to the MCs and the duration time. The flux, even in the minimum case, is larger than those of the brightest Galactic X-ray sources. Based on these facts, we conclude that the super-massive black hole, Sgr A*, exhibited a big-flare about a few hundred years ago and the luminosity of higher than 4x10^39 erg s^{-1}. The "X-ray echo" from Sgr B, located at a few hundred light-years from Sgr A*, now arrived at the Earth., Comment: 4 pages, 3 figures, accepted for publication in ApJL

We report the Suzaku observation of 1E 1740.7-2942, a black hole candidate called the "Great Annihilator" (GA). The high-quality spectrum of Suzaku provides the severest constraints on the parameters of the GA. Two clumpy structures are found around the GA in the line images of FeI Kalpha at 6.4 keV and SXV Kalpha at 2.45 keV. One clump named M359.23-0.04 exhibits the 6.4-keV line with an equivalent width of ~ 1.2 keV, and is associated with a molecular cloud in the radio CS(J=1-0) map. Thus the 6.4-keV line from M359.23-0.04 is likely due to X-ray fluorescence irradiated by an external X-ray source. The irradiating X-rays would be either the past flare of Sagittarius A* or the bright nearby source, the GA. The other clump named G359.12-0.05 is associated with the radio supernova remnant candidate G359.07-0.02. We therefore propose that G359.12-0.05 is an X-ray counterpart of G359.07-0.02. G359.12-0.05 has a thin thermal plasma spectrum with a temperature of kT ~ 0.9 keV. The plasma parameters of G359.12-0.05 are consistent with those of a single supernova remnant in the Galactic center region., Comment: 10 pages, 8 figures, accepted for publication in PASJ (Vol.62, No.4)

The K-shell emission line of neutral irons from the Galactic center (GC) region is one of the key for the structure and activity of the GC. The origin is still open question, but possibly due either to X-ray radiation or to electron bombarding to neutral atoms. To address this issue, we analyzed the Suzaku X-ray spectrum from the GC region of intense neutral iron line emission, and report on the discovery of Kalpha lines of neutral argon, calcium, chrome, and manganese atoms. The equivalent widths of these Kalpha lines indicate that the metal abundances in the GC region should be ~1.6 and ~4 of solar value, depending on the X-ray and the electron origins, respectively. On the other hand, the metal abundances in the hot plasma in the GC region are found to be ~1-2 solar. These results favor that the origin of the neutral Kalpha lines are due to X-ray irradiation., Comment: 7 pages, 5 figures, accepted for publication in PASJ (Vol.62, No.2, pp.423--429)

International audience; One of the remarkable features of the X‐ray emission from the Galactic center (GC) region is a Kα line at 6.4 keV from an Fe atom. Although some scenarios, such as photo‐ionization by external X‐rays (XRN) or collisional ionization by low energy cosmic‐ray electrons (LECRe) have been proposed, the origin of the 6.4 keV line is still an open question. We analyzed X‐ray data obtained by the X‐ray satellite Suzaku and discovered K‐shell lines of neutral Ar, Ca, Cr, and Mn atoms in addition to Fe and Ni. To explain the observed equivalent widths of the neutral lines, the elemental abundances are required to be ∼1.6 and ∼4 solar in the XRN and LECRe scenarios. On the other hand, the abundances of the various elements in the GC hot plasma were 1-2 solar. Ourresult suggests that the origin of the neutral K‐shell lines is the external X‐rays.

Diffuse X-rays from the Galactic center (GC) region were found to exhibit many K-shell lines from iron and nickel atoms in the 6--9 keV band. The strong emission lines seen in the spectrum are neutral iron K$\alpha$ at 6.4~keV, He-like iron K$\alpha$ at 6.7~keV, H-like iron Ly$\alpha$ at 6.9~keV, and He-like iron K$\beta$ at 7.8~keV. Among them, the 6.4~keV emission line is a probe of non-thermal phenomena. We have detected strong 6.4~keV emission in several giant molecular clouds, some of which were newly discovered by Suzaku. All the spectra exhibit large equivalent widths of 1-2~keV and absorption columns of $2-10\times 10^{23}\{\rm H\ cm}^{-2}$. We found time variability of diffuse 6.4~keV emission in the Sgr B2 region comparing the maps and spectra obtained from 1994 to 2005 with ASCA, Chandra, XMM-Newton and Suzaku. We also report discovery of K$\alpha$ lines of neutral argon, calcium, chrome, and manganese atoms in the Sgr~A region. We show that the equivalent width of the 6.4~keV emission line detected in X-ray faint region against the 6.4 keV-associated continuum (power-law component) is $\sim 800\ {\rm eV}$. These features are naturally explained by the X-ray reflection nebula scenario rather than the low energy cosmic-ray electrons scenario. On the other hand, a 6.4~keV clump, G~0.162$-$0.217, discovered at the south end of the Radio Arc has a small equivalent width of 6.4~keV emission line of $\sim200\ {\rm eV}$. The Radio Arc is a site of relativistic electrons. Thus, it is conceivable that the X-rays of G~0.162$-$0.217 are due to low energy cosmic-ray electrons, Comment: Invited Talk in "The Extreme sky: Sampling the Universe above 10 keV - extremesky2009", October 13-17, 2009 Otranto (Lecce) Italy. To be published in Proceedings of Science

We present a new methodology to derive the positions of the Sgr B molecular clouds (MCs) along the line of sight, as an application study of the Galactic center diffuse X-rays (GCDX). The GCDX is composed of hot plasma emission of about 7 keV and 1 keV temperatures, and non-thermal continuum emission including the 6.4 keV line from neutral irons. The former, the Galactic center plasma emission (GCPE), is uniformly distributed over 1 degree in longitude, while the latter is clumpy emission produced by Thomson scattering and fluorescence from MCs irradiated by external X-rays (the X-ray reflection nebula emission: XRNE). We examined the Suzaku X-ray spectra of the GCPE and XRNE near to the Sgr B MC complex, and found that the spectra suffer from two different absorptions of N_H (Abs1) >10^23 H cm^-2 and N_H (Abs2) ~6 x 10^22 H cm^-2. Abs1 is proportional to the 6.4 keV-line flux, and hence is due to the MCs, while Abs2 is typical of interstellar absorption toward the Galactic center. Assuming that the GCPE plasma is spherically-extended around Sgr A* with a uniform density and the same angular distribution of the two temperature components, we quantitatively estimated the line-of-sight positions of the MCs from the flux ratio the GCPE spectrum suffered by Abs1 and that with no Abs1. The results suggest that the Sgr B MCs are located at the near side of Sgr A* in the GCPE., 11 pages, 8 figures, accepted for publication in PASJ (Publications of the Astronomical Society of Japan)