Misalignment of the microquasar V4641 Sgr (SAX J1819.3--2525)

TL;DR

This paper investigates the misalignment between the black hole spin and the accretion disc in V4641 Sgr, using a warped disc model to explain inconsistent inclination measurements from jets and Fe Kα lines.

Contribution

The study applies an analytical warped disc model to V4641 Sgr, showing the inner disc is aligned with the black hole up to 900 Rg, clarifying the origin of inclination measurement discrepancies.

Findings

Inner disc aligned with black hole up to 900 Rg

Inconsistent inclination measurements explained by disc structure

Inner disc flat and aligned with black hole

Abstract

In the microquasar V4641 Sgr the spin of the black hole is thought to be misaligned with the binary orbital axis. The accretion disc aligns with the black hole spin by the Lense-Thirring effect near to the black hole and further out becomes aligned with the binary orbital axis. The inclination of the radio jets and the Fe$K\alpha$ line profile have both been used to determine the inclination of the inner accretion disc but the measurements are inconsistent. Using a steady state analytical warped disc model for V4641 Sgr we find that the inner disc region is flat and aligned with the black hole up to about $900 R_{\rm g}$. Thus if both the radio jet and fluorescent emission originates in the same inner region then the measurements of the inner disc inclination should be the same.