1999ApJ...519L.119K

We report the detection of both soft and hard excess X-ray emission in the cluster of galaxies A2199, based upon spatially resolved spectroscopy with data from the BeppoSAX, Extreme Ultraviolet Explorer, and ROSAT missions. The excess emission is visible at radii larger than 300 kpc and increases in strength relative to the isothermal component. The total 0.1-100 keV luminosity of this component is 15% of the cluster luminosity, but it dominates the cluster luminosity at high and low energies. We argue that the most plausible interpretation of the excess emission is an inverse Compton interaction between the cosmic microwave background and relativistic electrons in the cluster. The observed spatial distribution of the nonthermal component implies that there is a large halo of cosmic-ray electrons between 0.5 and 1.5 Mpc surrounding the cluster core. The prominent existence of this component has cosmological implications, since it is significantly changing our picture of clusters' particle acceleration history, dynamics between the thermal and relativistic media, and total mass budgets.