NuSTAR Observations of the Galaxy Cluster Abell 3667

TL;DR

This study uses NuSTAR data to analyze the hard X-ray emission in Abell 3667's center, concluding it is mainly thermal from merger heating, and estimates the cluster's magnetic field strength.

Contribution

First detailed NuSTAR analysis of Abell 3667's central X-ray emission, clarifying its thermal nature and setting magnetic field constraints.

Findings

Hard X-ray excess is thermal, modeled by two-temperature plasma.

High-temperature component linked to merger heating.

Magnetic field strength estimated at ≥0.2 μG.

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 $\sim 0.2 \, \mu$G 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.