On the Evidence for Extreme Gravity Effects in MCG-6-30-15

Abstract

We examine the unusual Fe-Kalpha line profile in MCG-6-30-15 observed by ASCA during a deep minimum in the source intensity. The intense red wing and depressed blue wing of the line have been interpreted as evidence for extreme gravitational redshifts in terms of emission from within six gravitational radii of a black hole. We find that the data do not uniquely support this interpretation and can be equally well explained by occultation of the continuum source and the putative line-emitting accretion disk, which we offer as an alternative hypothesis. Two problems with previous modeling were that the equivalent width of the line during the deep minimum was required to be unusually large (> 1 keV) and the line intensity was thought to increase as the source became dim. The occultation model does not suffer from these problems. Our results serve to highlight the hazards of over-interpreting observational results which have low statistical significance, to the extent that theoretical implications can become generally accepted when the data do not provide a strong case for them.