Broadening of the Iron emission line in MCG-6-30-15 by Comptonization

Abstract

We show that the Iron K emission line from MCG-6-30-15 could be broadened due to Comptonization by a surrounding highly ionized cloud with radius $\sim 10^{14}$ cms. We calculate the temperature of the cloud to be $\sim0.21\kev$, provided a reasonable estimate of the UV flux is made. The X-ray/$\gamma$-ray emission observed from the source is compatible with this model. Such a cloud should be highly ionized and strong absorption edges are not expected from the source (Fabian et al 1995). For a $\onlyten{6}\msol$ black hole the size of the could corresponds to about 300 Schwarzschild radius. The intrinsic line could then be emitted far from the black hole and gravitational red-shift and Doppler effects would be negligible. If the black hole mass is much larger than $\onlyten{6}\msol$, gravitational/Doppler red-shifts would also contribute significantly to the broadening. We argue that the broad red wing observed in the source does not by itself imply emission from regions close ($R < 5 r_s$) to the black hole. However, Comptonization cannot produce a double peak. The presence of such a feature is a clear sign of inner disk emission influenced by gravitational and Doppler effects, perhaps broadened by the Comptonization. We note that simultaneous broad band (2-100 keV) study of this source can also reveal (or rule out) the presence of such a Comptonizing cloud.