Radiation GRMHD simulations of M87: funnel properties and prospects for gap acceleration

We use the public code EBHLIGHT to carry out 3D radiative general relativistic magnetohydrodynamics (GRMHD) simulations of accretion on to the supermassive black hole in M87. The simulations self-consistently evolve a frequency-dependent Monte Carlo description of the radiation field produced by the accretion flow. We explore two limits of accumulated magnetic flux at the black hole (SANE and MAD), each coupled to several subgrid prescriptions for electron heating that are motivated by models of turbulence and magnetic reconnection. We present convergence studies for the radiation field and study its properties. We find that the near-horizon photon energy density is an order of magnitude higher than is predicted by simple isotropic estimates from the observed luminosity. The radially dependent photon momentum distribution is anisotropic and can be modeled by a set of point-sources near the equatorial plane. We draw properties of the radiation and magnetic field from the simulation and feed them into an analytic model of gap acceleration to estimate the very high energy (VHE) gamma-ray luminosity from the magnetized jet funnel, assuming that a gap is able to form. We find luminosities of similar to 1041 erg s(-1) for MAD models and for SANE models, which are comparable to measurements of M87's VHE flares. The time-dependence seen in our calculations is insufficient to explain the flaring behaviour. Our results provide a step towards bridging theoretical models of near-horizon properties seen in black hole images with the VHE activity of M87.

Automated summary

The study conducts 3D radiative GRMHD simulations of accretion onto the supermassive black hole in M87 using the public code EBHLIGHT. The results show anisotropic distributions of photon energy density and momentum, and estimate VHE gamma-ray luminosity from the magnetized jet funnel under MAD and SANE models. Time-dependence in the calculations is insufficient to explain the flaring behavior observed in M87.