Testing the Kerr metric with the iron line and the KRZ parametrization
Abstract
The spacetime geometry around astrophysical black holes is supposed to be well approximated by the Kerr metric, but deviations from the Kerr solution are predicted in a number of scenarios involving new physics. Broad iron Kα lines are commonly observed in the Xray spectrum of black holes and originate by Xray fluorescence of the inner accretion disk. The profile of the iron line is sensitively affected by the spacetime geometry in the strong gravity region and can be used to test the Kerr black hole hypothesis. In this paper, we extend previous work in the literature. In particular: i) as testmetric, we employ the parametrization recently proposed by Konoplya, Rezzolla, and Zhidenko, which has a number of subtle advantages with respect to the existing approaches; ii) we perform simulations with specific Xray missions, and we consider NuSTAR as a prototype of current observational facilities and eXTP as an example of the next generation of Xray observatories. We find a significant difference between the constraining power of NuSTAR and eXTP. With NuSTAR, it is difficult or impossible to constrain deviations from the Kerr metric. With eXTP, in most cases we can obtain quite stringent constraints (modulo we have the correct astrophysical model).
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 September 2016
 DOI:
 10.1088/14757516/2016/09/014
 arXiv:
 arXiv:1607.04893
 Bibcode:
 2016JCAP...09..014N
 Keywords:

 General Relativity and Quantum Cosmology;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 1+13 pages, 7 figures. v2: refereed version