NuSTAR Observations of Abell 2163: Constraints on Non-thermal Emission
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- Univ. of Utah, Salt Lake City, UT (United States)
- Naval Research Lab., Washington, DC (United States)
- Istituto di Astrofisica e Fiseca Cosmica-Milano Via Edoardo Bassini (Italy)
- Technical Univ. of Denmark, Lyngby (Denmark)
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
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 <4.0 × 10–12 erg s–1 cm–2 using the 1T+IC model and <1.6 × 10–12 erg s–1 cm–2 with the more physical 9T+IC model, both to 90% confidence levels. Here, combining these limits with 1.4 GHz diffuse radio data from the VLA, we find the average magnetic field strength to be >0.22 μG and >0.35 μG, respectively, providing the strongest constraints on these values in A2163 to date.
- Research Organization:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- AC02-76SF00515; 80NAAX19K0915
- OSTI ID:
- 1767940
- Journal Information:
- The Astrophysical Journal (Online), Vol. 906, Issue 2; ISSN 1538-4357
- Publisher:
- Institute of Physics (IOP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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