Suzaku Observations of Abell 1555 and Abell 1558: Searching for Non-Thermal Emission from Large-Scale Structure Formation

Abstract

We report on X-ray observations of two galaxy clusters, Abell 1555 and Abell 1558, with Suzaku, which are included in a large-scale filamentary structure and a supercluster, to search for non-thermal emission driven by shocks produced during structure formation. These two clusters were detected by Suzaku/XIS for the first time in the X-ray band of 0.5–7 keV. No significant flux has been detected by HXD in the energy band of 13–40 keV, and upper limits are reported. From an analysis of the XIS data, we found that the spectrum of A 1555 could be fit by a thermal plus power-law model, significantly better than a single-temperature pure thermal spectrum. If this power-law component is due to inverse-Compton scattering, the fraction of the total baryon energy imparted to non-thermal electrons is consistent with the typical value inferred from observations of other clusters. However, other scenarios (e.g., underlying AGNs, multi-temperature thermal models) cannot be excluded, and further investigation of this system is desired. Basic physical properties of A 1555 (e.g., total mass) are also reported.