X-Ray Iron Line Variability for the Model of an Orbiting Flare Above a Black Hole Accretion Disc

Abstract

The broad X-ray iron line, detected in many active galactic nuclei, is likely to be produced by fluorescence from the X-ray illuminated central parts of an accretion disc close to a supermassive black hole. The time-averaged shape of the line can be explained most naturally by a combination of special and general relativistic effects. Such line profiles contain information about the black hole spin and the accretion disc as well as the geometry of the emitting region and may help to test general relativity in the strong gravity regime. In this paper we embark on the computation of the temporal response of the line to the illuminating flux. Previous studies concentrated on the calculation of reverberation signatures from static sources illuminating the disc. In this paper we focus on the more physically justified case of flares located above the accretion disc and corotating with it. We compute the time dependent iron line taking into account all general relativistic effects and show that its shape is of very complex nature, and also present light curves accompanying the iron line variability. We suggest that future X-ray satellites like XMM or Constellation-X may be capable of detecting features present in the computed reverberation maps.

Light curve of a hotspot on equatorial orbit around Kerr black hole surrounded by reflective firewall

“…If there is a turning point n u = 1 in this case the geodesics is not divided into segments. We integrate system of diff equations ( 14), ( 17), (18), (19) down to λ = λ max and check for intersection with the hotspot.…”

“…There are many efforts available in the literature to study the hot spot. While we can not do justice to mention all the efforts, here we refer to some efforts such as [16][17][18][19][20][21][22][23]. A work dedicated to distinguish between the black holes and worm holes using hot spot can be found in [24].…”

Towards Gravitating Discs Around Stationary Black Holes

“…Certain spectral features (the iron Kα line in particular) of some active galactic nuclei (a celebrated example is the Seyfert 1 galaxy MCG-6-30-15) have been interpreted as originating as close to the very centre as a few to a few dozens of Schwarzschild radii, 8 so they may well represent data from the strongest fields ever met (see [107] for a review, and e.g. [266,267,155,88] for models and interpretation issues). The iron lines have already been discovered in the X-ray spectrum of several Galactic microquasars ( [224] and references therein).…”