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[13.07] Hard power-law emission components in the X-ray spectra of elliptical galaxies

T. Di Matteo (Harvard-Smithsonian Center for Astrophysics), S.W. Allen (Institute of Astronomy, Cambridge, UK)

We report the first detections of hard power-law emission components in the X-ray spectra of six giant elliptical galaxies with previously-reported evidence for supermassive black holes in their nuclei. The observations were carried out with the ASCA satellite.The mean photon index, \Gamma=1.2, and luminosities of the detected power-law components (L_X,1-10 ~2.6 \times 10⁴⁰-2.1 \times 10⁴² ergs^-1) suggest that the emission originates in the accretion process around the central black holes and is most plausibly due to low-radiative efficiency accretion. Detailed models and important implications of this discovery are discussed.

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