Abstract
We construct a relativistic reflection model in a non-Kerr spacetime in which, depending on the value of the deformation parameter of the metric, there are black hole solutions with spin parameter |a_*| > 1. We apply our model to fit Suzaku data of four Seyfert galaxies (Ton S180, Ark 120, 1H0419–577, and Swift J0501.9–3239). These galaxies host at the center supermassive black holes that were previously interpreted as near-extremal Kerr black holes. For Ton S180 and 1H0419–577, our measurements are still consistent with the Kerr hypothesis. For Ark 120 and Swift J0501.9–3239, the Kerr solution is not recovered at 3-sigma . We discuss our results and possible systematic uncertainties in the model.
Highlights
In 4-dimensional Einstein’s theory of general relativity, uncharged black holes are described by the Kerr solution [1] and are completely characterized by two parameters, which are associated, respectively, to the mass M and the spin angular momentum J of the compact object
If we want to test the nature of astrophysical black holes with electromagnetic techniques, the most logical method would be compare the predictions of general relativity with those of another theory of gravity in which uncharged black holes are not described by the Kerr solution
Our study found that the spacetime metric around the central compact object was consistent with the Kerr solution, with remarkably strong constraints on the deformation parameters α13 and α22
Summary
In 4-dimensional Einstein’s theory of general relativity, uncharged black holes are described by the Kerr solution [1] and are completely characterized by two parameters, which are associated, respectively, to the mass M and the spin angular momentum J of the compact object. If we want to test the nature of astrophysical black holes with electromagnetic techniques, the most logical method would be compare the predictions of general relativity with those of another theory of gravity in which uncharged black holes are not described by the Kerr solution.. Black holes that were previously found to be spinning at a near-maximum spin are the most suitable sources for this kind of tests, because the inner edge of the accretion disk can be very close to the compact object, relativistic features in the reflection spectrum are maximized, and it is possible to break the parameter degeneracy and get good measurements of the spacetime metric.
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