NuSTAR hard X-ray observations of the merging cluster of galaxies RX J1347.5-1145

Abstract

Mergers of galaxy clusters are the most energetic events in the Universe after the Big Bang and strongly affect the cluster structure. Aiming for understanding the nature of intracluster medium in a violent merger, we observed one of the most X-ray luminous clusters, RX J1347.5-1145 (z=0.45) with the NuSTAR satellite. First, to estimate the background accurately, we simulated the background  considering the position dependence of each component including the aperture component of the telescope. Second, based on the image analysis, the surface brightness distributions for two different regions were examined. Thirdly, we fit the energy spectra assuming three models for the excess component in the north east region, i.e., thermal emission, non-thermal emission, or thermal emission + non-thermal emission. Based on the hard X-ray imaging and spectral analyses, we obtained the two major results. First, we detected the spatially-extended hard X-ray emission from the cluster for the first time. Second, we confirmed the presence of extremely hot gas with 19.6(-1.9,+2.3)(-1.2,+1.7) keV in the south-east region with the high accuracy. Also, we found the 3σ upper limit on the non-thermal flux, 7 × 10⁻¹³ erg/cm²/s in the 12–60 keV band. Combining the limit with the observation of the mini halo at 1.4 GHz, we obtained the lower limit of the cluster magnetic field to be 0.05 µG