Results from a second Rossi X-Ray Timing Explorer observation of the Coma Cluster

The Rossi X-Ray Timing Explorer satellite observed the Coma Cluster for ∼177 ks during 2000 November and December, a second observation motivated by the intriguing results from the first ∼87 ks observation in 1996. Analysis of the new data set confirms that thermal emission from isothermal gas does not provide a good fit to the spectral distribution of the emission from the inner 1° radial region. While the observed spectrum may be fitted by emission from gas with a substantial temperature gradient, it is more likely that the emission also includes a secondary nonthermal component. If so, nonthermal emission comprises ∼8% of the total 4-20 keV flux. Interpreting this emission as due to Compton scattering of relativistic electrons (which produce the known extended radio emission) by the cosmic microwave background radiation, we determine that the mean, volume-averaged magnetic field in the central region of Coma is B ∼ 0.1-0.3 μG.