Abstract
Suzaku performed observations of 3 regions in and around the Shapley supercluster, a region located between A 3558 and A 3556, at
$\sim\ $
0.9 times the virial radii of both clusters, and two other regions at 1
$^\circ$
and 4
$^\circ$
away from the first pointing. The 4
$^\circ$
-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. The upper limit for the redshifted O VIII K
$\alpha$
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
$\sim\ $
380 (
$Z/$
0.1
$\ Z_{\odot}$
)
$^{-1/2}$
(
$L/$
3 Mpc)
$^{-1/2}$
, assuming
$T$
$=$
3
$\times$
10
$^{6}$
K. We found excess continuum emission in the 1
$^\circ$
-offset and on-filament regions, represented by thermal models with
$ kT\sim 1$
keV and
$\sim\ $
2 keV, respectively. The redshifts of both 0 and that of the supercluster (0.048) are consistent with the observed spectra. The
$\sim\ $
1 keV emission can also be fitted with Ne-rich Galactic (zero redshift) thin thermal emission. The radial intensity profile of the 2 keV component suggests contributions from A 3558 and A 3556, but with significant steepening of the intensity slope in the outer region of A 3558. Finally, we summarized the previous Suzaku search for the WHIM, and discussed the feasibility of constraining the WHIM. An overdensity of
$\lt\ $
400 could be detectable using O VII and O VIII emission lines in a range of 1.4
$\times$
10
$^{6}$
K
$\lt\ $
$T$
$\lt\ $
5
$\times$
10
$^{6}$
K or a continuum emission in a relatively high-temperature range of
$T$
$\gt$
5
$\times$
10
$^{6}$
K with the Suzaku XIS. The non-detection with Suzaku suggests that a typical line-of-sight average overdensity is
$\lt\ $
400.
