X‐Ray Measurements of Nonthermal Emission from the Abell 1367 Galaxy Cluster Using theRossi X‐Ray Timing Explorer

Abstract

Observations with the Rossi X-Ray Timing Explorer (RXTE), the Advanced Satellite for Astrophysics and Cosmology, and ROSAT have been used to search for X-ray emission produced by the inverse Compton process in the Abell 1367 galaxy cluster. The three data sets provide a high-quality spectrum which extends from 0.4 to 20 keV, allowing accurate separation of thermal and nonthermal components. In the cases of both the cluster's radio halo relic and radio galaxy 3C 264, the detection of nonthermal emission is model dependent. Nonthermal emission from the relic is detected using the RXTE Proportional Counter Array with a flux of ~0.010-0.019 photons cm-2 keV-1 s-1 at 1 keV, when the thermal emission is modeled with a single thermal component. However, modeling the thermal emission with two thermal components provides a better fit to the data and obviates the need for a nonthermal power-law component. We also find that thermal emission is a physically plausible origin for the second component. Using two thermal components to model the spectrum gives an upper limit of 3.3 × 10-3 photons cm-2 keV-1 s-1 on nonthermal X-ray emission from the radio relic region. We derive an average intracluster magnetic field of ≥0.84 μG for this region. This value is consistent with the radial field derived from Faraday rotation studies of noncooling flow clusters. For the central region of the intracluster medium, we find an upper limit of 1.08 × 10-3 photons cm-2 keV-1 s-1 at 1 keV for nonthermal emission. Joint fitting of the data sets gives a detection of nonthermal emission for 3C 264 of 1.21 × 10-4 to 2.45 × 10-4 photons cm-2 keV-1 s-1 at 1 keV, using a single thermal component. However, as with the radio relic region, two thermal components provide a much better fit to the spectrum and give an upper limit of less than 5.3 × 10-5 photons cm-2 keV-1 s-1 at 1 keV. Combining the X-ray upper limit with the radio spectrum gives an average magnetic field greater than 0.41 μG.