Search for X-Ray Emission Associated with the Shapley Supercluster with
  Suzaku
  Suzaku performed observations of 3 regions in and around the Shapley
supercluster: a region located between A3558 and A3556, at ~0.9 times the
virial radii of both clusters, and two other regions at 1{\deg}and 4{\deg}away
from the first pointing. The 4{\deg}-offset observation was used to evaluate
the Galactic foreground emission. We did not detect significant redshifted
Oxygen emission lines (O VII and O VIII) in the spectra of all three pointings,
after subtracting the contribution of foreground and background emission. An
upper limit for the redshifted O VIII Ka line intensity of the warm-hot
intergalactic medium (WHIM) is 1.5 \times 10^-7 photons s^-1 cm^-2 arcmin^-2,
which corresponds to an overdensity of ~380 (Z/0.1 Z_solar)^{-1/2} (L/3
Mpc)^{-1/2}, assuming T=3\times10^6 K. We found excess continuum emission in
the 1{\deg}-offset and on-filament regions, represented by thermal models with
kT ~1 keV and ~2 keV, respectively. The redshifts of both 0 and that of the
supercluster (0.048) are consistent with the observed spectra. The ~1 keV
emission can be also fitted with Ne-rich Galactic (zero redshift) thin thermal
emission. Radial intensity profile of 2 keV component suggests contribution
from A3558 and A3556, but with significant steepening of the intensity slope in
the outer region of A3558. Finally, we summarized the previous Suzaku search
for the WHIM and discussed the feasibility of constraining the WHIM. An
overdensity of < 400 can be detectable using O VII and O VIII emission lines in
a range of 1.4\times10^6 K < T < 5\times10^6 K or a continuum emission in a
relatively high temperature range T > 5\times10^6 K with the Suzaku XIS. The
non detection with Suzaku suggests that typical line-of-sight average
overdensity is < 400.
