Conflicting Disk Inclination Estimates for the Black Hole X-Ray Binary XTE J1500−564

Abstract

The dynamical characteristics of XTE J1550−564, a black hole X-ray binary, are well established, and the broadband spectral evolution of the source has been well studied. Its orbital inclination is known to be high, at ~75°, with the jet estimated to align well with the orbital axis. We explore simultaneous observations made with the Advanced Satellite for Cosmology and Astrophysics and Rossi X-ray Timing Explorer covering the 1–200 keV band during the early stages of the first outburst of XTE J1550−564 in its hard-intermediate state on 1998 September 23/24. We show that the most up-to-date reflection models applied to these data yield an inclination estimate much lower than that found in previous studies at ~40°, grossly disagreeing with the dynamically estimated orbital inclination. We discuss the possible explanations for this disagreement and its implications for reflection models, including possible physical scenarios in which either the inner disk is misaligned with both the binary orbit and the outer jet or the inner accretion flow, corona, and/or jet have vertical structure that leads to lower inferred disk inclination through various physical means.

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