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Published March 20, 2020 | Accepted Version + Published
Journal Article Open

Evidence for Returning Disk Radiation in the Black Hole X-Ray Binary XTE J1550–564


We explore the accretion properties of the black hole X-ray binary XTE J1550−564 during its outbursts in 1998/99 and 2000. We model the disk, corona, and reflection components of X-ray spectra taken with the Rossi X-ray Timing Explorer, using the relxill suite of reflection models. The key result of our modeling is that the reflection spectrum in the very soft state is best explained by disk self-irradiation, i.e., photons from the inner disk are bent by the strong gravity of the black hole and reflected off the disk surface. This is the first known detection of thermal disk radiation reflecting off the inner disk. There is also an apparent absorption line at ~6.9 keV, which may be evidence of an ionized disk wind. The coronal electron temperature (kT_e) is, as expected, lower in the brighter outburst of 1998/99, explained qualitatively by more efficient coronal cooling due to irradiating disk photons. The disk inner radius is consistent with being within a few times the innermost stable circular orbit throughout the bright-hard-to-soft states (10 s of r_g in gravitational units). The disk inclination is low during the hard state, disagreeing with the binary inclination value, and very close to 90° in the soft state, recovering to a lower value when adopting a blackbody spectrum as the irradiating continuum.

Additional Information

© 2020 The American Astronomical Society. Received 2019 December 31; revised 2020 February 21; accepted 2020 February 26; published 2020 March 27. We thank the referee for the diligent comments that helped to improve this paper. J.A.G. acknowledges support from NASA grant NNX15AV31G and from the Alexander von Humboldt Foundation. R.M.T.C. has been supported by NASA grant 80NSSC177K0515. V.G. is supported through the Margarete von Wrangell fellowship by the ESF and the Ministry of Science, Research and the Arts Baden-Württemberg. This research has made use of data, software and/or web tools obtained from the High Energy Astrophysics Science Archive Research Center (HEASARC), a service of the Astrophysics Science Division at NASA/GSFC and of the Smithsonian Astrophysical Observatory's High Energy Astrophysics Division. This research has made use of ISIS functions (ISISscripts) provided by ECAP/Remeis observatory and MIT (http://www.sternwarte.uni-erlangen.de/isis/). Facilities: RXTE (PCA; Jahoda et al. 1996), HEASARC. Software: XSPEC v.12.10.1c (Arnaud 1996), XILLVER (García & Kallman 2010; García et al. 2013), RELXILL (v1.2.0; García et al. 2014; Dauser et al. 2014).

Attached Files

Published - Connors_2020_ApJ_892_47.pdf

Accepted Version - 2002.11873.pdf


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August 22, 2023
October 19, 2023