Using iron line reverberation and spectroscopy to distinguish Kerr and non-Kerr black holes

Abstract

The iron K$\alpha$ line commonly observed in the X-ray spectrum of both stellar-mass and supermassive black hole candidates is produced by the illumination of a cold accretion disk by a hot corona. In this framework, the activation of a new flaring region in the hot corona imprints a time variation on the iron line spectrum. Future X-ray facilities with high time resolution and large effective areas may be able to measure the so-called 2-dimensional transfer function; that is, the iron line profile detected by a distant observer as a function of time in response to an instantaneous flare from the X-ray primary source. This work is a preliminary study to determine if and how such a technique can provide more information about the spacetime geometry around the compact object than the already possible measurements of the time-integrated iron line profile. Within our simplified model, we find that a measurement of iron line reverberation can improve constraints appreciably given a sufficiently strong signal, though that most of the information is present in the time-integrated spectrum. Our aim is to test the Kerr metric. We find that current X-ray facilities and data are unable to provide strong tests of the Kerr nature of supermassive black hole candidates. We consider an optimistic case of $10^5$ iron line photons from a next-generation data set. With such data, the reverberation model improves upon the spectral constraint by an order of magnitude.

1+24 pages, 17 figures. v3: refereed version

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• Circular Orbits Structure and Thin Accretion Disks around Kerr Black Holes with Scalar Hair
• Iron K$\alpha$ line of boson stars
• Strong gravitational lensing by a Konoplya-Zhidenko rotating non-Kerr compact object
• Constraining the Johannsen deformation parameter ${\epsilon }_3$ with black hole X-ray data
• Silhouette and spectral line profiles in the special modification of the Kerr black hole geometry generated by quintessential fields
• Constraining the Kerr parameters via X-ray reflection spectroscopy
• Iron line reverberation mapping in Ghasemi-Nodehi-Bambi background
• Using Simulations of Black Holes to Study General Relativity and the Properties of Inner Accretion Flow