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, knowing the IC flux can provide a lower limit for the magnetic field strength of the cluster. We model the cluster emission using four different models: single temperature (T), two temperature (2T), multi-temperature (9T), and temperature+power law component (T+PO). We find that the global NuSTAR spectrum is consistent with pure thermal emission, in particular by the 2T model, with a global temperature of kT = 11.77 ± 0.13 keV. From the T+PO model, we constrain the upper limit for IC scattering emission to be 1.62x10^-12 erg s^-1 cm^-2, which provides a lower bound for the magnetic field strength of 0.22μG or 0.35μG if we replace the T with 9T.