Search for WHIM around A2744 using Suzaku

We present the results from the Suzaku satellite of the surrounding region of a galaxy cluster, A2744, at \(z=0.3\). To search for oxygen emission lines from the warm-hot intergalactic medium (WHIM), we analyzed X-ray spectra from two northeast regions 2.2-3.3 and 3.3-4.4 Mpc from the center of the cluster, which offers the first test on the presence of a WHIM near the typical accretion shock radius (\(\sim 2r_{200}\)) predicted by hydrodynamical simulations. For the 2.2-3.3 Mpc region, the spectral fit significantly (99.2% significance) improved when we include OVII and OVIII lines in the spectral model. A comparable WHIM surface brightness was obtained in the 3.3-4.4 Mpc region and the redshift of OVIII line is consistent with \(z=0.3\) within errors. The present results support that the observed soft X-ray emission originated from the WHIM. However, considering both statistical and systematic uncertainties, OVIII detection in the northeast regions was marginal. The surface brightness of the OVIII line in \({\rm 10^{-7} photons\,cm^{-2}s^{-1}arcmin^{-2}}\) was measured to be \(2.7\pm 1.0\), \(2.1 \pm 1.2\) for the 2.2-3.3, 3.3-4.4 Mpc regions, giving the upper limit on the baryon overdensity of \(\delta = 319 (