# Conflicting disk inclination estimates for the black hole X-ray binary XTE J1550-564

## TL;DR

This study analyzes simultaneous X-ray observations of XTE J1550-564, revealing a discrepancy between reflection model inclination estimates and dynamical measurements, suggesting possible misalignment or complex disk structures.

## Contribution

It demonstrates that current reflection models can significantly underestimate disk inclination, highlighting the need to consider physical misalignments or vertical structures in accretion flows.

## Key findings

- Reflection models estimate inclination at ~40°, lower than the known ~75°.
- Discrepancy suggests possible misalignment between inner disk and binary orbit.
- Implications for reflection modeling and understanding of accretion geometry.

## Abstract

XTE J1550-564 is a black hole X-ray binary for which the dynamical characteristics are well established, and the broadband spectral evolution of the source has been well studied. Its orbital inclination is known to be high, at $\sim75^{\circ}$, with the jet estimated to align well with the orbital axis. We explore simultaneous observations made with ASCA and RXTE, covering the $1$--$200$~keV band, during the early stages of the first outburst of XTE J1550-564 in its hard-intermediate state, on 1998-09-23/24. We show that the most up-to-date reflection models, applied to these data, yield an inclination estimate much lower than found in previous studies, at $\sim40^{\circ}$, 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 both with binary orbit and the outer jet, or either the inner accretion flow, corona, and/or jet have vertical structure which leads to lower inferred disk inclination through various physical means.