Testing the Kerr nature of black hole candidates using iron line reverberation mapping in the Cardoso-Pani-Rico framework

Abstract

The iron Kα 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 r 3 , which is only weakly informed by a time-integrated observation.

Testing black hole candidates with electromagnetic radiation

“…In the left panels, r 3 mainly affects the propagation of the photons in the spacetime, but the impact on the timeintegrated iron line measurement is weak. More details on the constraints on the CPR deformation parameters from the iron line can be found in Jiang et al (2015bJiang et al ( , 2016.…”

“…Iron line reverberation mapping in a non-Kerr background was investigated in Jiang et al (2015aJiang et al ( , 2016. Fig.…”

Colibrì: taking the pulse of black holes and neutron stars

“…High-resolution spectral fitting of the X-ray emission, especially of the Fe-line profile, provides information on the strong-field gravity effects on the orbiting plasma and its dynamics, from which radii can be inferred in units of the gravitational radius, as well as the spin of the black hole and the inclination angle of the system. The possibility of performing reverberation mapping, which yields distances in absolute units given by the light travel time, simultaneously to spectral fitting would therefore provide a test of the Kerr metric itself, as well as a measurement of the mass of the compact object [25,26]. Although the total spectral features of reverberation are relativistically broadened in general, high energy and timing resolution combined would allow slicing the emission in both the spectral and time domain, which could reveal sharp features, broadened not by the bulk motion of the disk material but by thermal and turbulent motion within the disk with v/c ∼ 10 −3 or smaller as shown by the green curves in Figure 1.…”

Thin accretion disks and charged rotating dilaton black holes

“…In a recent work [75], the authors have studied thin accretion disks around electrically and magnetically charged Gibbons-Maeda-Garfinkle-Horowitz-Strominger (GMGHS) black holes. Also, k α iron line analysis and continuum-fitting method are used to distinguish different astrophysical objects through their accretion disks [76][77][78][79]. In this paper we consider static and slowly rotating charged dilaton black holes and study the properties of thin accretion disks around them.…”