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We present the results from the Suzaku satellite of the surrounding region ofa galaxy cluster, A2744, at $z=0.3$. To search for oxygen emission lines fromthe warm-hot intergalactic medium (WHIM), we analyzed X-ray spectra from twonortheast regions 2.2-3.3 and 3.3-4.4 Mpc from the center of the cluster, whichoffers the first test on the presence of a WHIM near the typical accretionshock radius ($\sim 2r_{200}$) predicted by hydrodynamical simulations. For the2.2-3.3 Mpc region, the spectral fit significantly (99.2% significance)improved when we include OVII and OVIII lines in the spectral model. Acomparable WHIM surface brightness was obtained in the 3.3-4.4 Mpc region andthe redshift of OVIII line is consistent with $z=0.3$ within errors. Thepresent results support that the observed soft X-ray emission originated fromthe WHIM. However, considering both statistical and systematic uncertainties,OVIII detection in the northeast regions was marginal. The surface brightnessof the OVIII line in ${\rm 10^{-7} photons\,cm^{-2}s^{-1}arcmin^{-2}}$ wasmeasured to be $2.7\pm 1.0$, $2.1 \pm 1.2$ for the 2.2-3.3, 3.3-4.4 Mpcregions, giving the upper limit on the baryon overdensity of $\delta = 319(<443)$, $283 (<446)$, respectively. This is comparable with previousobservations of cluster outskirts and their theoretical predictions. The futureprospect for WHIM detection using the Athena X-IFU micro-calorimeter is brieflydiscussed here. In addition, we also derived the ICM temperature distributionof A2744 to detect a clear discontinuity at the location of the radio relic.This suggests that the cluster has undergone strong shock heating by massaccretion along the filament.

Search for WHIM around A2744 using Suzaku