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| Paper: |
The Galactic Center Diffuse X-rays |
| Volume: |
439, The Galactic Center: a Window to the Nuclear Environment of Disk Galaxies |
| Page: |
418 |
| Authors: |
Koyama, K. |
| Abstract: |
One of the remarkable features of the Galactic diffuse X-ray
is the emission of strong K-shell transition lines (Kα) from neutral
(Fe I), He-like
(Fe xxv) and H-like (Fe xxvi) irons at energies of 6.4 keV, 6.7 keV
and 7.0 keV, respectively.
We make the longitude and latitude profiles of the fluxes of these lines and
the continuum flux in the 5–10 keV band, for the wide region around the
Galactic center (GC), Sgr A*.
The profiles are fit with a two-dimensional function, composing
a compact central region (Galactic center diffuse X-rays; GCDX)
and a largely extended emission (Galactic ridge diffuse X-rays: GRDX).
The profile of the GCDX has e-folding values of 0°.5 and 0°.2
in the longitude and latitude directions, while those of
the GRDX are ∼30° and 1°.7, respectively.
In the GCDX, the 6.4 keV and 6.7 keV line fluxes are not
proportional to the continuum flux in the 5–10 keV band.
On the other hand, the sum of the 6.4 keV plus
6.7 keV line fluxes with the ratio of 1:2 is nicely proportional
to the continuum flux.
We therefore phenomenologically decompose the continuum flux of the GCDX
into the 6.4 keV- and 6.7 keV-associated continua with the flux
ratio of 1:2.
The GCDX spectrum is also fit by a 6.5 keV-temperature
plasma and a power-law continuum of the photon index 1.4 plus
Gaussian lines at 6.4 keV (Fe I-Kα) and 7.05 keV (Fe I-Kβ).
The fluxes of these two
components are nearly the same.
Based on these facts, we estimate the flux ratio of the diffuse and
the integrated point sources as ∼6:1.
In contrast to the 6.7 keV and 7.0 keV line fluxes, that of 6.4 keV is
not uniform but more clumpy. From the Radio Arc region, we find
K-shell lines from the neutral atoms of Ar, Ca, Cr and Mn,
in addition to the already known lines of Fe and Ni.
The equivalent widths of these lines are consistent with
the X-ray irradiation scenario with 1–2 solar abundances.
The bright 6.4 keV clump Sgr B2 is found to be variable in
∼10 years time scale. We hence suspect that Sgr A*
exhibited a large flare about 300 years ago with the
variability time scale of about 10 years. |
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