Abstract
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, 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.
Highlights
Some of the most luminous astrophysical sources, such as active galactic nuclei, X-ray binaries, and long gamma-ray bursts, are all powered by the accretion of gas onto black holes (BHs)
As a first step toward better understanding X-ray reverberation from super-Eddington accretion flows and motivated by the framework described in Kara et al (2016), we study the fluorescent Fe Kα emission line profiles derived from state-ofthe-art super-Eddington disk simulations
In this Letter, we have presented the first theoretical investigation of the Fe Kα fluorescent line profile produced when a realistic super-Eddington accretion disk, resolved in generalrelativistic radiation magnetohydrodynamic (GRRMHD) simulations, is irradiated by a lamppost corona
Summary
Some of the most luminous astrophysical sources, such as active galactic nuclei, X-ray binaries, and long gamma-ray bursts, are all powered by the accretion of gas onto black holes (BHs). We study in detail the profile of a super-Eddington disk, previously simulated in Dai et al (2018), and calculate the reflection surface of the coronal emission, which is embedded in the optically thick winds, and its properties (Section 2). As simulated illustrated disk with in Figure an accretion rate of 2(b), the ionization level is several orders of magnitudes higher than that of the theoretical thin disk (usually with x 100 erg cm s-1 outside the ISCO; see e.g., Reynolds & Begelman 1997) This is mainly because the density of the gas in the wind is much more dilute in comparison to a dense thin accretion disk. This high ionization interval strongly favors the production of the hot and warm Fe Kα lines with rest-frame energies of 6.97 and 6.7 keV instead of the cold 6.4 keV Fe line, usually assumed to be produced from thin disks (Ballantyne & Ramirez-Ruiz 2001)
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