NuSTAR Observations of the Galaxy Cluster Abell 3667

Abstract

We present an analysis of the hard X-ray emission from the central region of Abell 3667 using deep NuSTAR observations. While previous studies on the nature of the hard X-ray excess have been controversial, our analysis of the central region suggests that the excess is primarily thermal, best described by a two-temperature (2T) model, with the high-temperature component likely arising from merger-induced heating. This interpretation contrasts with some earlier suggestions of non-thermal emission due to inverse Compton scattering of relativistic electrons. Additionally, we set a lower limit on the magnetic field strength of ∼ 0.2 μG in the central region, consistent with values found in other dynamically active clusters and compatible with those inferred from equipartition and Faraday rotation measurements. Since our study is focused on the central region of the cluster, further high-resolution observations of the outer regions will be critical to fully disentangle the thermal and non-thermal contributions to the X-ray.