Feasibility Study of Lense-Thirring Precession in LS I +61303

TL;DR

This study explores whether Lense-Thirring precession caused by a slowly rotating compact object can explain the rapid changes in ejecta angle observed in the microquasar LSI+61303, considering the system's accretion disk properties.

Contribution

It provides a feasibility analysis of Lense-Thirring precession as the mechanism behind observed jet variations in LSI+61303, linking disk truncation and precession periods.

Findings

Lense-Thirring precession period could be a few days for a slow rotator.

Tidal forces induce a precession period of over one year.

The truncated disk radius is estimated at 300 r_g based on QPO observations.

Abstract

Very recent analysis of the radio spectral index and high energy observations have shown that the two-peak accretion/ejection microquasar model applies for LSI+61303. The fast variations of the position angle observed with MERLIN and confirmed by consecutive VLBA images must therefore be explained in the context of the microquasar scenario. We calculate what could be the precessional period for the accretion disk in LSI+61303 under tidal forces of the Be star (P_{tidal-forces}) or under the effect of frame dragging produced by the rotation of the compact object (P_{Lense-Thirring}). P_{tidal-forces}$ is more than one year. P_{Lense-Thirring} depends on the truncated radius of the accretion disk, $R_{tr}$. We determined R_{tr}=300 r_g for observed QPO at 2 Hz. This value is much above the few $r_g$, where the Bardeen-Petterson effect should align the midplane of the disk. For this truncated radius of the accretion disk P_{Lense-Thirring} for a slow rotator results in a few days. Therefore, Lense-Thirring precession induced by a slowly rotating compact object could be compatible with the daily variations of the ejecta angle observed in LSI+61303.