NuSTAR Observations of Abell 2163: Constraints on Non-thermal Emission

Randall A. Rojas Bolivar, Daniel R. Wik, Simona Giacintucci, Fabio Gastaldello, Allan Hornstrup, Niels-Jorgen Westergaard, Grzegorz Madejski

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    Since the first non-thermal reports of inverse Compton (IC) emission from the intracluster medium (ICM) of galaxy clusters at hard X-ray energies, we have yet to unambiguously confirm IC emission in observations with newer facilities. RXTE detected IC emission in one of the hottest known clusters, Abell 2163 (A2163), a massive merging cluster with a giant radio halo—the presumed source of relativistic electrons IC scattering CMB photons to X-ray energies. The cluster’s redshift (z ∼ 0.2) allows its thermal and non-thermal radio emission to fit the field of view of the Nuclear Spectroscopic Telescope Array (NuSTAR), permitting a deep observation capable of confirming or ruling out the RXTE report. The IC flux provides constraints on the average magnetic field strength in a cluster. To determine the global diffuse IC emission in A2163, we fit its global NuSTAR spectrum with four models: single- (1T) and two-temperature (2T), 1T+power-law component (T+IC), and multi-temperature+power law (9T+IC). Each represents different characterizations of the thermal ICM emission, with power-law components added to represent IC emission. We find that the 3–30 keV spectrum can be described by purely thermal emission, with a global average temperature of kT = (11.8 ± 0.2) keV. The IC flux is constrained to 0.22 μG and >0.35 μG, respectively, providing the strongest constraints on these values in A2163 to date.
    Original languageEnglish
    Article number87
    JournalAstrophysical Journal Supplement Series
    Issue number2
    Number of pages13
    Publication statusPublished - 2021


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