Jet Tilt Instability from Stream-Disk Interactions in MAD Disks

Abstract

Magnetically arrested accretion disks (MADs) around a rapidly rotating black hole (BH) have been proposed as a model for jetted tidal disruption events (TDEs). However, the stream and disk interact strongly at times, and this will lead to different dynamics than expected in the standard MAD model. Here we employ global GRMHD simulations of a MAD disk interacting with an injected stream with a penetrating pericenter $R_p\sim 10 r_g$ and a range of density contrasts $f_\rho\equiv \rho_d/\rho_s$, or how dense the disk is relative to the stream. We demonstrate for the first time that a MAD or semi-MAD state can be sustained and jets powered by the BH spin can be produced even when the stream is much denser than the disk, i.e. in the first month(s) of a jetted TDE. We also demonstrate that the strength of the self-intersection shock decreases as $f_\rho$, and time, increases. The jet or funnel can become significantly tilted (by $10-30^\circ$) due to the self-intersection outflow when $f_\rho \leq 0.1$. In models with a powerful jet and $f_\rho\leq 0.01$, the tilted jet interacts with and ultimately tilts the disk by as much as 23 degrees from the incoming stream and this tilted state is stable for the duration of the simulation. As $f_\rho$ increases, the tilt of the jet and disk is expected to realign with the BH spin once $f_\rho \geq 0.1$. The jet tilt could rapidly realign due to outer disk collapse or the self-intersection radius increasing. Our results provide an alternative explanation for the observed X-ray jet shut-off in days-weeks in jetted TDEs.