RXTE Investigation into Extended Hard X-ray Emission from Elliptical Galaxies

Abstract

We present results of the first RXTE investigation of hard X-ray emission from normal elliptical galaxies. Joint spectral analysis of RXTE PCA and ASCA GIS data for NGC 4472 and NGC 4649 reveals the presence of about 5 10^-12 erg cm^-2 s^-1 of 2-10 keV emission emanating from a region outside of the optical galaxy, and of a spectral hardness intermediate between the galactic hot interstellar gas and X-ray binary components. A large fraction of this emission originates in the Virgo intracluster medium (ICM) and we present constraints on the ICM temperature and metallicity in the vicinity of these two galaxies. However, the diffuse flux is significantly greater than expected based on the soft X-ray intensity measured with ROSAT, allowing for the possible presence of an additional diffuse non-thermal component. We also derive new constraints on the integrated X-ray binary emission from these two galaxies, and on the presence of a nuclear flat-spectrum point source.