Unlocking Pandora's Secrets: Probing the Thermodynamics of Abell 2744

Abstract

Abell 2744 (Pandora's Cluster) is a massive galaxy cluster undergoing multiple mergers, characterized by a highly disturbed X-ray morphology, elevated intracluster medium (ICM) temperatures, and several radio relics associated with merger driven shocks. We present NuSTAR observations of Abell 2744 aimed at mapping its thermodynamic structure and constraining the presence of inverse Compton (IC) scattering from relativistic electrons. We measure the temperature distribution across the cluster and identify a prominent shock front with a Mach number of $\mathcal{M} = 1.58^{+0.42}_{-0.30}$, aligning with the southeastern boundary of the radio halo. The global NuSTAR spectra are modeled with single- and two-temperature thermal components, as well as thermal plus power-law models to test for IC emission. The spectra are well described by purely thermal models with an average temperature of $kT \approx 11$ keV, and we find no significant evidence for non-thermal hard X-ray emission. We derive a 90\% confidence upper limit on the $20-80$ keV IC flux of $ F_{\rm nt} < 2.31 \times 10^{-12} erg~s^{-1}~cm^{-2}$. Combining this with 1.5 GHz diffuse radio measurements from the VLA, we estimate a lower limit on the average magnetic field strength of $B > 0.2 \ \rm{μG}$.