Suzaku performed observations of 3 regions in and around the Shapley supercluster : a region located between A3558 and A3556 , 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 \emissiontype VII and O \emissiontype VIII ) in the spectra of all three pointings , after subtracting the contribution of foreground and background emission .
An upper limit for the redshifted O \emissiontype 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 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 \emissiontype VII and O \emissiontype VIII emission lines in a range of 1.4 \times 10 ^ { 6 } ~ { } \mathrm { K } < T < 5 \times 10 ^ { 6 } ~ { } \mathrm { K } or a continuum emission in a relatively high temperature range T > 5 \times 10 ^ { 6 } ~ { } \mathrm { K } with the Suzaku XIS .
The non detection with Suzaku suggests that typical line-of-sight average overdensity is < 400 .