X-Ray Fluorescence from Super-Eddington Accreting Black Holes

Abstract

X-ray reverberation has proven to be a powerful tool capable of probing the innermost region of accretion disks around compact objects. Current theoretical effort generally assumes that the disk is geometrically thin, optically thick and orbiting with Keplerian speed. Thus, these models cannot be applied to systems where super-Eddington accretion happens because the thin disk approximation fails in this accretion regime. Furthermore, state-of-the-art numerical simulations show that optically thick winds are launched from the super-Eddington accretion disks, and thereby changing the reflection geometry significantly from the thin disk picture. We carry out theoretical investigations on this topic by focusing on the Fe Kα fluorescent lines produced from super-Eddington disks, and show that their line profiles are shaped by the funnel geometry and wind acceleration. We also systematically compare the Fe line profiles from super-Eddington thick disks to those from thin disks, and find that the former are substantially more blueshifted and symmetric in shape. These results are consistent with the observed Fe Kα line from the jetted tidal disruption event, Swift J1644, in which a transient super-Eddington accretion disk was formed out of stellar debris. Therefore, careful analysis of the Fe Kα line profile can be used to identify systems undergoing super-Eddington accretion.

Reverberation in Tidal Disruption Events: Dust Echoes, Coronal Emission Lines, Multi-wavelength Cross-correlations, and QPOs

“…The extremely high isotropic luminosity and the detection of strong radio emission from Swift J1644+57 suggest that this is a TDE with a jet along our line of sight, and a face-on accretion flow. The highly blueshifted iron K line and corresponding reverberation lag can be well described by reprocessing off of a Compton thick, outflowing disc wind with a velocity of > 0.1c and ∼ 30 deg opening angle (Kara et al 2016b;Lu et al 2017;Thomsen et al 2019). The iron K lag is marginally better described (> 98% confidence) by an asymmetrically broadened line with some gravitational redshifted over a symmetric Gaussian.…”

Reverberation mapping of active galactic nuclei: From X-ray corona to dusty torus

“… Taylor and Reynolds (2018) studied the impulse response functions assuming a lamppost corona irradiating a more physical, nonzero scale height disk, following a Novikov-Thorne disk profile. More recently, Thomsen et al. (2019) calculated the anticipated iron line and reverberation signature off the electron scattering photosphere of a general relativistic radiation magnetohydrodynamic simulation of a super-Eddington accretion flow.…”

The origin of X-ray emission in the gamma-ray emitting narrow-line Seyfert 1 1H 0323+342

“…A very recent study by Thomsen et al (2019) makes use of this funnel geometry to make a detailed comparison between the iron line profiles of thin disks and those of a geometrically thick supper-Eddington disk. In particular, they show that, in each type of disk, photons emitted from different radii have different contributions to the line profile.…”