NuSTAR Observations of ABELL 2163: Constraining Non-Thermal Emission

Since the first non-thermal detections of Inverse Compton (IC) emission in galaxy clusters at hard X-ray energies, we have yet to unambiguously confirm IC in follow-up observations. Claims of large IC fluxes from the 10' extent of Abell 2163, a massive merging cluster at z = 0.2, make it the next best chance of confirming a previous IC detection with NuSTAR. Additionally, recently available deep XMM data indicate extreme temperature variations (10-20 keV), the hottest of which are likely due to shocks. However, the XMM spectra suffer from variable Galactic absorption across the cluster, which can be avoided with NuSTAR's harder energy band. We find that the global NuSTAR spectrum is consistent with pure thermal emission, with a global temperature of 11.77 keV +/- 0.13 keV. Our model provides a constraint on IC emission of 1.62 x 10^-12 erg s^-1 cm^-2 as well as a value for the magnetic field of the cluster, B > 0.22 μG or B > 0.35 μG using the normalization obtained from a nine temperature model.