Constraint of Non-Thermal X-Ray Emission from the On-Going Merger Cluster Abell 3376 with Suzaku

Abstract

Clusters of galaxies are among the best candidates for particle acceleration sources in the universe, a signature of which is non-thermal hard X-ray emission from the accelerated relativistic particles. We present early results on Suzaku observations of non-thermal emission from Abell 3376, which is a nearby on-going merger cluster. Suzaku observed the cluster twice, while focusing on the cluster center containing the diffuse radio emission to the east, and a cluster peripheral region to the west. For both observations, we detected no excess hard X-ray emission above the thermal cluster emission. An upper limit on the non-thermal X-ray flux of 2.1 $\times$ 10$^{-11}$ erg cm$^{-2}$s$^{-1}$ (15–50 keV) at the 3$\sigma$ level from a 34$^\prime$$\times$ 34$^\prime$ region, derived with the Hard X-ray Detector (HXD), is similar to that obtained with the BeppoSAX/PDS. Using the X-ray Imaging Spectrometer (XIS) data, the upper limit on the non-thermal emission from the West Relic is independently constrained to be $<$1.1 $\times$ 10$^{-12}$ erg s$^{-1}$ cm$^{-2}$ (4–8 keV) at the 3$\sigma$ level from a 122 arcmin$^2$ region. Assuming Compton scattering between relativistic particles and the cosmic microwave background photons, the intracluster magnetic field $B$ is limited to be $>$0.03$\mu$G (HXD) and $>$0.10$\mu$G (XIS).