1305.5409 (Cosimo Bambi)

Measuring the Kerr spin parameter of a non-Kerr compact object with the
continuum-fitting and the iron line methods    [PDF]

Cosimo Bambi

Under the assumption that astrophysical black hole candidates are the Kerr black holes of general relativity, the continuum-fitting method and the analysis of the K$\alpha$ iron line are today the only available techniques capable of providing a relatively reliable estimate of the spin parameter of these objects. If we relax the Kerr black hole hypothesis and we try to test the nature of black hole candidates, we find that there is a strong correlation between the measurement of the spin and possible deviations from the Kerr solution. The properties of the radiation emitted in a Kerr spacetime with spin parameter $a_*$ are indeed very similar, and practically indistinguishable, from the ones of the radiation emitted around a non-Kerr object with different spin. In this paper, I address the question whether measuring the Kerr spin with both the continuum-fitting method and the K$\alpha$ iron line analysis of the same object can be used to claim the Kerr nature of the black hole candidate in the case of consistent results. The answer is more likely negative: if the object is not a Kerr black hole but we assume it is, the two techniques may anyway provide a very similar result.

View original: http://arxiv.org/abs/1305.5409