Non-Thermal and Thermal Hard X-ray Emission from Clusters of Galaxies

Some recent Suzaku and XMM-Newton results on the thermal and non-thermal hard X-ray emission from clusters of galaxies are presented. The Coma cluster has the brightest cluster radio halo in the sky. We do not find significant evidence for non-thermal inverse Compton hard X-ray emission in Coma.Instead, we find that the Suzaku and XMM-Newton spectra are best explained by hot thermal gas in the cluster. Our upper limit on the non-thermal hard X-ray emission in Coma is well below the previous claimed detections with RXTE and BeppoSAX. However, since the field of view of the Suzaku HXD PIN detector is smaller than that of RXTE and BeppoSAX (although still bigger than the angular size of the radio halo), our upper limit and the previous detections might be consistent if the non-thermal emission comes from a very extended region which is much larger than the radio halo. Abell 3667 is a merging cluster with two cluster radio relics. The northwest radio relic is the brightest diffuse cluster radio source in the sky (brightest halo or relic). Our Suzaku observations show evidence for a very hot thermal component (kT > 13 keV) in the center of this cluster. This emission may be associated with merger shocks. The Suzaku spectra do not show clear evidence for non-thermal inverse Compton hard X-ray emission from the NW radio relic. We recently obtained a deep XMM observation of the region of the NW radio relic. The XMM image shows a surface brightness discontinuity at the outer edge of the radio relic. The image and spectra of this region are consistent with the jump being a merger shock with a Mach number of about 2. Alternatively, the X-ray emission in this region might be non-thermal emission from the radio relic. Our Suzaku and XMM observations imply that the magnetic field in the relic is B > or approximately 3 micro G, which is a surprisingly large field at such a large distance (about 2.2 Mpc) from the center of a cluster. This indicates that there is a nontrivial contribution of non-thermal pressure in this region.