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.