Magnetized funnel properties and prospects for gap acceleration from radiation GRMHD simulations of M87

In this work, we use the Radiative General Relativistic Magnetohydrodynamics (GRMHD) code ebhlight to carry out first-principles simulations of the accretion flow and radiation field near the horizon of a supermassive black hole. Paired with different electron heating schemes, the code follows the self-consistent emission and propagation of a large number of Monte Carlo photons. We perform simulations for both SANE (Standard and Normal Evolution) and MAD (Magnetically Arrested Disk) configurations of M87, and examine the properties of the resulting photon distribution and spectrum. We find an order of magnitude higher near-horizon photon energy density than simple isotropic estimates from the observed luminosity in the millimeter wavelengths. The photon distribution depends on the radius, and can be approximately explained by a simple radiation model consisting of point-sources near the equatorial plane. Using the soft photon distribution near the horizon, we compute the very-high-energy (VHE) gamma-ray luminosity from pair-accelerating gaps in the jet funnel. We find luminosities of ~10⁴¹ erg/s for MAD models and ~2×10⁴⁰ erg/s for SANE models, which are comparable to what was observed in the VHE flares from M87. Our results constitute a first attempt at bridging near-horizon properties relevant for Event Horizon Telescope (EHT) images with expectations for the VHE emission from M87. The radiation field anisotropy could have implications for particle-in-cell (PIC) studies aiming to model the gap formation and particle acceleration, and in turn for assessing the viability of particle acceleration near the black hole event horizon.