GRRMHD simulations of tidal disruption event accretion discs around supermassive black holes: jet formation, spectra, and detectability

We report results from general relativistic radiation magnetohydrodynamics (GRRMHD) simulations of a super-Eddington black hole (BH) accretion disc formed as a result of a tidal disruption event (TDE). We consider the fiducial case of a solar mass star on a mildly penetrating orbit disrupted by a supermassive BH of mass 10^6 M_⊙, and consider the epoch of peak fallback rate. We post-process the simulation data to compute viewing angle-dependent spectra. We perform a parameter study of the dynamics of the accretion disc as a function of BH spin and magnetic flux, and compute model spectra as a function of the viewing angle of the observer. We also consider detection limits based on the model spectra. We find that an accretion disc with a relatively weak magnetic field around the BH [so-called SANE (Standard and Normal Evolution) regime of accretion] does not launch a relativistic jet, whether or not the BH is rotating. Such models reasonably reproduce several observational properties of non-jetted TDEs. The same is also true for a non-rotating BH with a strong magnetic field (magnetically arrested accretion disc, MAD regime). One of our simulations has a rapidly rotating BH (spin parameter 0.9) as well as a MAD accretion disc. This model launches a powerful relativistic jet, which is powered by the BH spin energy. It reproduces the high-energy emission and jet structure of the jetted TDE Swift J1644 + 57 surprisingly well. Jetted TDEs may thus correspond to the subset of TDE systems that have both a rapidly spinning BH and MAD accretion.