Nonthermal X‐Ray Emission: An Alternative to Cluster Cooling Flows?

We report the results of experiments aimed at reducing the major problem with cooling flow models of rich cluster X-ray sources, i.e., the fact that most of the cooled gas or its products have not been found. Here we show that much of the X-ray emission usually attributed to cooling flows can, in fact, be modeled by a power-law component which is indicative of a source(s) other than thermal bremsstrahlung from the intracluster medium. We find that adequate simultaneous fits to ROSAT PSPC and ASCA GIS/SIS spectra of the central regions of 10 clusters are obtained for two-component models that include a thermal plasma component that is attributable to hot intracluster gas and a power-law component that is likely generated by compact sources and/or extended nonthermal emission. For five of the clusters that purportedly have massive cooling flows, the best-fit models have power-law components that contribute ~30% of the total flux (0.14-10.0 keV) within the central 3'. Because cooling flow mass deposition rates are inferred from X-ray fluxes, our finding opens the possibility of significantly reducing cooling rates.