The Nature of Extended Hard X-ray Emission from the Coma Cluster as Observed by the Swift BAT

Details The Nature of Extended Hard X-ray Emission from the Coma Cluster as Observed by the Swift BAT The Nature of Extended Hard X-ray Emission from the Coma Cluster as Observed by the Swift BAT

Feb 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010head...11.3410w&link_type=abstract

American Astronomical Society, HEAD meeting #11, #34.10; Bulletin of the American Astronomical Society, Vol. 41, p.712

Astronomy and Astrophysics

Astronomy

Scientific paper

Coexisting with the X-ray emitting, thermal gas in the intracluster medium (ICM) of galaxy clusters is a nonthermal phase of made up of relativistic electrons, ions, and magnetic fields. This phase is revealed through observations of radio halos and relics, which are diffuse, Mpc-scale structures due to synchrotron emission. The energy tied up in the nonthermal phase, and therefore its dynamical importance, cannot be determined without a measurement of the average magnetic field strength B, which cannot be inferred from the synchrotron emission alone. One way to find B is to detect inverse Compton (IC) emission from the same synchrotron-emitting electrons, particularly at hard X-ray energies. In our previous joint Suzaku HXD and XMM-Newton spectral analysis of the Coma cluster, which hosts the brightest radio halo and for which a detection of IC emission has been claimed (Rephaeli & Gruber 2002; Fusco-Femiano et al. 2004), we do not confirm this emission and instead derive an upper limit on the nonthermal flux 2.5 times below the previous detections. Due to the Suzaku HXD's smaller field of view, however, all observations would still be consistent if the IC emission is more extended than the radio halo. We present a test of this hypothesis with data from the Swift BAT instrument, for which we have developed a method for analyzing moderately extended emission. We find that the detected emission is extended and consistent with a thermal origin, and that upper limits to diffuse, nonthermal emission rule out at least some models of IC production. Using this method, we also introduce a joint XMM-Swift spectral survey of hard X-ray emission for all radio halo and relic clusters, as well as for the flux-limited HIFLUGCS cluster sample, which will allow us to place average constraints on the nonthermal phase of the ICM.

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