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Register a new userThe K-shell Line Distribution of Heavy Elements along the Galactic Plane Observed with Suzaku
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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$7 keV plasma.
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We have surveyed spatial profiles of the Fe K$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 $3.8pm0.3$ $(timeform{0D.2}<|l|<timeform{1D.5})$ or $19pm6$ $(|l|<timeform{0D.2})$ times excess over the best-fit SMD model in the GRXE region. Thus Fe emissiontype{XXV} K$alpha$ in the GCDX is hardly explained by the same origin of the GRXE. In the case of point source origin, a new population with the extremely strong Fe emissiontype{XXV} K$alpha$ line is required. An alternative possibility is that the majority of the GCDX is truly diffuse optically thin thermal plasma.
We report the Suzaku/XIS results of the Galactic oxygen-rich supernova remnant (SNR), G292.0+1.8, a remnant of a core-collapse supernova. The X-ray spectrum of G292.0+1.8 consists of two type plasmas, one is in collisional ionization equilibrium (CIE) and the other is in non-equilibrium ionization (NEI). The CIE plasma has nearly solar abundances, and hence would be originated from the circumstellar and interstellar mediums. The NEI plasma has super-solar abundances, and the abundance pattern indicates that the plasma originates from the supernova ejecta with a main sequence of 30-35 Msolar. Iron K-shell line at energy of 6.6 keV is detected for the first time in the NEI plasma.
We present observations of a transient He-like Fe K alpha absorption line in Suzaku observations of the black hole binary Cygnus X-1 on 2011 October 5 near superior conjunction during the high/soft state, which enable us to map the full evolution from the start and the end of the episodic accretion phenomena or dips for the first time. We model the X-ray spectra during the event and trace their evolution. The absorption line is rather weak in the first half of the observation, but instantly deepens for ~10 ks, and weakens thereafter. The overall change in equivalent width is a factor of ~3, peaking at an orbital phase of ~0.08. This is evidence that the companion stellar wind feeding the black hole is clumpy. By analyzing the line with a Voigt profile, it is found to be consistent with a slightly redshifted Fe XXV transition, or possibly a mixture of several species less ionized than Fe XXV. The data may be explained by a clump located at a distance of ~10^(10-12) cm with a density of ~10^((-13)-(-11)) g cm^-3, which accretes onto and/or transits the line-of-sight to the black hole, causing an instant decrease in the observed degree of the ionization and/or an increase in density of the accreting matter. Continued monitoring for individual events with future X-ray calorimeter missions such as ASTRO-H and AXSIO will allow us to map out the accretion environment in detail and how it changes between the various accretion states.
Galactic infrared (IR) bubbles, which have shell-like structures in the mid-IR wavelengths, are known to contain massive stars near their centers. IR bubbles in inner Galactic regions ($|$l$|leq$ 65$^{circ}$, $|$b$|leq$ 1$^{circ}$) have so far been studied well to understand the massive star formation mechanisms. In this study, we expand the research area to the whole Galactic plane (0$^{circ}leq$ l $<$360$^{circ}$, $|$b$|leq$ 5$^{circ}$), using the AKARI all-sky survey data. We limit our study on large bubbles with angular radii of $>1$ to reliably identify and characterize them. For the 247 IR bubbles in total, we derived the radii and the covering fractions of the shells, based on the method developed in citet{Hattori2016}. We also created their spectral energy distributions, using the AKARI and Herschel photometric data, and decomposed them with a dust model, to obtain the total IR luminosity and the luminosity of each dust component, i.e., polycyclic aromatic hydrocarbons (PAHs), warm dust and cold dust. As a result, we find that there are systematic differences in the IR properties of the bubbles between inner and outer Galactic regions. The total IR luminosities are lower in outer Galactic regions, while there is no systematic difference in the range of the shell radii between inner and outer Galactic regions. More IR bubbles tend to be observed as broken bubbles rather than closed ones and the fractional luminosities of the PAH emission are significantly higher in outer Galactic regions. We discuss the implications of these results for the massive stars and the interstellar environments associated with the Galactic IR bubbles.
In order to elucidate origin of the Galactic Ridge X-ray Emission, we analyzed Suzaku data taken at various regions along the Galactic plane and studied their Fe-K emission line features. Suzaku resolved the Fe line complex into three narrow lines at ~6.4 keV,~6.7 keV and ~6.97 keV, which are K-lines from neutral (or low-ionized), He-like, and H-like iron ions, respectively. The 6.7 keV line is clearly seen in all the observed regions and its longitudinal distribution is consistent with that determined from previous observations. The 6.4 keV emission line was also found in various Galactic plane regions (b~0). Differences in flux ratios of the 6.4 keV/6.7 keV and 6.97 keV/6.7 keV lines between the Galactic plane and the Galactic center regions are studied and its implication is discussed.
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