Direct Wind Accretion and Jet Launch in Binary Systems

TL;DR

This study explores how wind accretion onto a rotating black hole in binary systems can launch powerful jets via the Blandford-Znajek mechanism without forming an accretion disk, using 2D GRMHD simulations.

Contribution

It demonstrates that under certain conditions, black hole jets can be powered by wind accretion without accretion disks, and provides estimates of jet power and variability.

Findings

Jet power can reach about 10% of accreted rest energy.

Jets are modulated on sub-second timescales due to magnetic flux accumulation.

No thermal X-ray signatures are expected from this accretion scenario.

Abstract

In this paper we study the wind accretion onto a rotating black hole in the close binary system harboring a young massive star. It is shown that the angular momentum of the accreted stellar wind material is not sufficient for the formation of an accretion disk. On the other hand, in the considered conditions the Blanford-Znajek mechanism can be activated, thus powerful jets can be launched in the direction of the rotation axis of the black hole. Importantly, no observational signatures of accretion, as typically seen from the thermal X-ray emission from the accretion disks, are expected in the suggested scenario. Here, properties of the generated jet are studied numerically in the framework of a 2D general relativity magnetohydrodynamical approach. Due to the accumulation of the magnetic flux at the black hole horizon, the jet power is expected to be modulated on a sub-second time-scale. Although the intervals between jet active phases depend on the magnetic flux escape from the black hole horizon (which can be modeled self-consistently only using a 3D code), a general estimate of the averaged jet power is obtained. It is expected that for the black hole rotation, expected in stellar binary system (the dimensionless rotation parameter a=0.5), approximately 10% of the accreted rest energy can be channeled into the jets. In the specific case of the gamma-ray binary system LS 5039, the obtained jet luminosity can be responsible for the observed GeV radiation if one invokes Doppler boosting, which can enhanced the apparent flux from the system.