Relativistic X-Ray Reverberation from Super-Eddington Accretion Flow
Author(s)
Thomsen, Lars Lund; Dai, Lixin; Kara, Erin; Reynolds, Chris
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<jats:title>Abstract</jats:title>
<jats:p>X-ray reverberation is a powerful technique that uses the echoes of the coronal emission reflected by a black hole (BH) accretion disk to map out the inner disk structure. While the theory of X-ray reverberation has been developed almost exclusively for standard thin disks, reverberation lags have recently been observed from likely super-Eddington accretion sources such as the jetted tidal disruption event Swift J1644+57. In this paper, we extend X-ray reverberation studies into the regime of super-Eddington accretion with a focus on investigating the lags in the fluorescent Fe K<jats:italic>α</jats:italic> line region. We find that the coronal photons are mostly reflected by the fast and optically thick winds launched from the super-Eddington accretion flow, and this funnel-like reflection geometry produces lag–frequency and lag–energy spectra with unique observable characteristics. The lag–frequency spectrum exhibits a step-function-like decline near the first zero-crossing point. As a result, the magnitude of the lag scales linearly with the BH mass for a large parameter space, and the shape of the lag–energy spectrum remains almost independent of the choice of frequency bands. Not only can these features be used to distinguish super-Eddington accretion systems from sub-Eddington systems, but they are also key for constraining the reflection geometry and extracting parameters from the observed lags. When fitting the observed reverberation lag of Swift J1644+57 to our modeling, we find that the super-Eddington disk geometry is slightly preferred over the thin disk geometry, and we obtain a BH mass of 5–6 × 10<jats:sup>6</jats:sup>
<jats:italic>M</jats:italic>
<jats:sub>☉</jats:sub> and a coronal height around 10 <jats:italic>R<jats:sub>g</jats:sub>
</jats:italic>.</jats:p>
Date issued
2022-02Department
MIT Kavli Institute for Astrophysics and Space ResearchJournal
Astrophysical Journal
Publisher
American Astronomical Society
Citation
Thomsen, Lars Lund, Dai, Lixin, Kara, Erin and Reynolds, Chris. 2022. "Relativistic X-Ray Reverberation from Super-Eddington Accretion Flow." The Astrophysical Journal, 925 (2).
Version: Final published version
ISSN
0004-637X
1538-4357