An X-Ray Face-on View of the Sgr B Molecular Clouds Observed with Suzaku
  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.
