Inclination and relativistic effects in the outburst evolution of black hole transients

TL;DR

This study investigates how orbital inclination influences the outburst evolution of black hole transients, revealing that relativistic effects cause observable differences in spectral properties based on viewing angle.

Contribution

It is the first systematic analysis of inclination effects on black hole transient outbursts, incorporating relativistic considerations to explain spectral differences.

Findings

Low-inclination systems have softer spectra.

Accretion discs appear cooler at low inclination.

Relativistic effects explain inclination-dependent spectral variations.

Abstract

We have systematically studied the effect of the orbital inclination in the outburst evolution of black hole transients. We have included all the systems observed by the Rossi X-ray timing explorer in which the thermal, accretion disc component becomes strongly dominant at some point of the outburst. Inclination is found to modify the shape of the tracks that these systems display in the colour/luminosity diagrams traditionally used for their study. Black hole transients seen at low inclination reach softer spectra and their accretion discs look cooler than those observed closer to edge-on. This difference can be naturally explained by considering inclination dependent relativistic effects on accretion discs.