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

TL;DR

This study uses advanced 3D radiative GRMHD simulations to analyze the near-horizon environment of M87's black hole, estimating gamma-ray luminosity and exploring implications for jet physics and high-energy emission.

Contribution

It presents the first self-consistent radiative GRMHD simulations of M87's accretion flow, incorporating electron heating models and analyzing photon and magnetic field properties near the horizon.

Findings

Near-horizon photon energy density is much higher than simple estimates.

Radiation field is anisotropic and modeled by point sources near the equator.

Estimated gamma-ray luminosities match observed VHE flares in M87.

Abstract

We use the public code ebhlight to carry out 3D radiative general relativistic magnetohydrodynamics (GRMHD) simulations of accretion onto 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 sub-grid 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 $\rm \sim 10^{41} \, erg \, s^{-1}$ for MAD models and $\rm \sim 2\times 10^{40} \, erg \, s^{-1}$ 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 behavior. Our results provide a step towards bridging theoretical models of near-horizon properties seen in black hole images with the VHE activity of M87.