Investigating the hard X-ray emission from the hottest Abell cluster A2163 with Suzaku

Naomi Ota (1) , K. Nagayoshi (2) , G. W. Pratt (3, 4) , T. Kitayama (5) , T. Oshima (6) , T. H. Reiprich (7)

1 Nara Women's University
2 ISAS - Institute of Space and Astronautical Science
3 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
4 DAP - Département d'Astrophysique (ex SAP)
5 Toho University
6 Nobeyama Radio Observatory
7 AlfA - Argelander Institute for Astronomy

Context. We present the results from Suzaku of the hottest Abell galaxy cluster A2163 at z = 0.2.Aims. To study the physics of gas heating in cluster mergers, we investigated hard X-ray emission from the merging cluster A2163, which hosts the brightest synchrotron radio halo. Methods. We analyzed hard X-ray emission spectra accumulated from two-pointed Suzaku observations. Non-thermal hard X-ray emission should result from the inverse Compton scattering of relativistic electrons by photons in the cosmic microwave background. To measure this emission, the dominant thermal emission in the hard X-ray band must be modeled in detail. To this end, we analyzed the combined broadband X-ray data of A2163 collected by Suzaku and XMM-Newton, assuming single- and multi-temperature models for thermal emission and the power-law model for non-thermal emission. Comparing the non-thermal hard X-ray flux to radio synchrotron emission, we also estimated the magnetic field in the cluster. Results. From the Suzaku data, we detected significant hard X-ray emission from A2163 in the 12–60 keV band at the 28σ level (or at the 5.5σ level if a systematic error of the non-X-ray background model is considered). The Suzaku HXD spectrum alone is consistent with the single-temperature thermal model of gas temperature kT = 14 keV. From the XMM-Newton data, we constructed a multi-temperature model including a very hot (kT = 18 keV) component in the north-east region. Incorporating the multi-temperature and the power-law models into a two-component model with a radio-band photon index, where Γ = 2.18, the 12–60 keV energy flux of non-thermal emission is constrained within 5.3 ± 0.9 (±3.8) × 10-12 erg s-1cm-2 (the first and second errors refer to the 1σ statistical and systematic uncertainties, respectively). The 90% upper limit of detected inverse Compton emission is marginal (FNT < 1.2 × 10-11 erg s-1cm-2 in the 12–60 keV band). The estimated magnetic field in A2163 is B > 0.098 μG. While the present results represent a three-fold increase in the accuracy of the broadband (0.3–60 keV) spectral model of A2163, more sensitive hard X-ray observations are needed to decisively test for the presence of hard X-ray emission due to inverse Compton emission.

Keywords: galaxies: clusters: individual: A2163; galaxies: clusters: intracluster medium; X-rays: galaxies: clusters; cosmology: observations

Domains: Astrophysics [astro-ph]

Naomi Ota, K. Nagayoshi, G. W. Pratt, T. Kitayama, T. Oshima, et al.. Investigating the hard X-ray emission from the hottest Abell cluster A2163 with Suzaku. Astronomy and Astrophysics - A&A, 2014, 562, pp.A60. ⟨10.1051/0004-6361/201322878⟩. ⟨cea-01162428⟩