https://doi.org/10.1140/epjc/s10052-020-7916-8
Regular Article - Theoretical Physics
Testing Ghasemi-Nodehi–Bambi spacetime with continuum-fitting method
School of Astronomy, Institute for Research in Fundamental Sciences (IPM), P. O. Box 19395-5531, Tehran, Iran
* e-mail: mghasemin@ipm.ir
Received:
22
December
2019
Accepted:
8
April
2020
Published online:
12
May
2020
The continuum-fitting method is the analysis of the thermal spectrum of the geometrically thin and optically thick accretion disk around stellar-mass black holes. A parametrization aiming to test the Kerr nature of astrophysical black holes was proposed in Ghasemi-Nodehi and Bambi in EPJC 76:290, 2016. The metric contains 11 parameters in addition to the mass and spin parameters. One can recover the Kerr case by setting all parameters to one. In this paper, I study the continuum-fitting method in a Ghasemi-Nodehi–Bambi background. I show the impact of each of the parameters on the spectra. I then employ 
studies and show that using the continuum-fitting method all parameters of Ghasemi-Nodehi–Bambi spacetime are degenerate. However, the parameter 
can be constrained in the case of a high spin value and the Ghasemi-Nodehi–Bambi black hole as reference. This degeneracy means that the spectra of the Kerr case cannot be distinguished from spectra produced in Ghasemi-Nodehi–Bambi spacetime. This is a problem as regards measuring the spin of astrophysical black holes and constrain possible deviations from the Kerr case of General Relativity.
© The Author(s), 2020
