X-ray spectropolarimetric measurements of the Kerr metric

Abstract

It is thought that the spacetime geometry around black hole candidates is described by the Kerr solution, but an observational confirmation is still missing. Today, the continuum-fitting method and the analysis of the iron K$\alpha$ line cannot unambiguously test the Kerr paradigm because of the degeneracy among the parameters of the system, in the sense that it is impossible with current X-ray data to distinguish a Kerr black hole from a non-Kerr object with different values of the model parameters. In this paper, we study the possibility of testing the Kerr nature of black hole candidates with X-ray spectropolarimetric measurements. Within our simplified model that does not include the effect of returning radiation, we find that it is impossible to test the Kerr metric and the problem is still the strong correlation between the spin and possible deviations from the Kerr geometry. Moreover, the correlation is very similar to that of other two techniques, which makes the combination of different measurements not very helpful. Nevertheless, our results cannot be taken as conclusive and, in order to arrive at a final answer, the effect of returning radiation should be properly taken into account.

12 pages, 8 figures. v2: refereed version

References in corpus (11)

• A Metric for Rapidly Spinning Black Holes Suitable for Strong-Field Tests of the No-Hair Theorem
• A code to compute the emission of thin accretion disks in non-Kerr space-times and test the nature of black hole candidates
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• Challenging the paradigm of singularity excision in gravitational collapse
• Probing the space-time geometry around black hole candidates with the resonance models for high-frequency QPOs and comparison with the continuum-fitting method
• Constraints on the spacetime geometry around 10 stellar-mass black hole candidates from the disk's thermal spectrum
• Broad K$\alpha$ iron line from accretion disks around traversable wormholes
• Using iron line reverberation and spectroscopy to distinguish Kerr and non-Kerr black holes
• Note on the effect of a massive accretion disk in the measurements of black hole spins
• Attempt to find a correlation between the spin of stellar-mass black hole candidates and the power of steady jets: relaxing the Kerr black hole hypothesis
• Note on the Cardoso-Pani-Rico parametrization to test the Kerr black hole hypothesis

Cited by in corpus (10)

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• Testing General Relativity's No-Hair Theorem with X-Ray Observations of Black Holes
• X-ray spectropolarimetric signature of a warped disk around a stellar-mass black hole
• Electromagnetic signatures of strong-field gravity from accreting black holes
• Testing Gravity with Black Hole X-Ray Data
• Tests of General Relativity using black hole X-ray data
• Decoding Cygnus X-2: The Critical Role of Reflection in IXPE Data