Testing the Kerr nature of black hole candidates using iron line reverberation mapping in the CPR framework

TL;DR

This paper demonstrates that iron line reverberation mapping significantly improves constraints on deviations from the Kerr black hole metric, especially for parameters weakly constrained by time-integrated spectra.

Contribution

It extends previous work by analyzing iron line reverberation mapping within the CPR framework to better test the Kerr hypothesis.

Findings

Reverberation mapping enhances constraints on spacetime deviations.

Time information improves sensitivity to the deformation parameter ^r_3.

Reverberation mapping outperforms time-integrated spectra in constraining the metric.

Abstract

The iron K$\alpha$ line commonly observed in the X-ray spectrum of black hole candidates is produced by X-ray fluorescence of the inner accretion disk. This line can potentially be quite a powerful tool to probe the spacetime geometry around these objects and test the Kerr black hole hypothesis. In a previous paper, we studied the ability to constrain possible deviations from the Kerr solution from the standard time-integrated iron line spectrum within the Cardoso-Pani-Rico framework. In the present work, we expand on that study and consider iron line reverberation mapping in the CPR framework. That is, we consider the time-evolution of the iron line profile in response to fluctuations in the X-ray primary source. Our simulations clearly show that the time information in reverberation mapping can better constrain the background metric than the time-integrated approach, and this is true, notably, for the deformation parameter $\epsilon^r_3$, which is only weakly informed by a time-integrated observation.