Launching Jets in Tidal Disruption Events: Magnetic Flux Advection and Plasma Loading

Abstract

A tidal disruption event (TDE) occurs when a star approaches a black hole (BH) and is disrupted by its tidal forces. Although several hundred TDEs have been identified to date, only a small fraction are accompanied by relativistic jets. These jets are thought to be Poynting-flux-dominated outflows powered by the Blandford--Znajek (BZ) mechanism. However, the origin of the magnetic flux and plasma needed to power BZ jets remain unclear. In this Letter, we propose a scenario in which magnetic flux is initially stored in a pre-existing low-Eddington accretion disk around BH, and is subsequently advected toward the BH by the super-Eddington accretion flow formed after the stellar disruption. We show that stars with low densities, such as red giants, can supply sufficient magnetic flux to power a BZ jet. Once sufficient magnetic flux accumulates near the BH, an equatorial current sheet forms where magnetic reconnection produces high-energy gamma rays. We find that photon--photon pair production by these gamma rays supplies the BH magnetosphere with sufficient plasma to launch and sustain a BZ jet. We further show that this mechanism simultaneously provides enough radiating particles to account for the observed prompt emission.