Double Compton and Cyclo-Synchrotron in Super-Eddington Disks, Magnetized Coronae, and Jets

TL;DR

This paper extends a relativistic radiation magnetohydrodynamic code to include key emission and absorption processes, revealing their significant roles in the radiative properties of super-Eddington accretion disks, coronae, and jets.

Contribution

It introduces new extensions to the HARMRAD code to model thermal cyclo-synchrotron and double Compton processes, providing insights into their effects on accretion disk and jet physics.

Findings

Double Compton dominates bremsstrahlung within 15r_g at high accretion rates.

Double Compton and cyclo-synchrotron regulate temperatures in coronae and jets.

An optically thin corona with T~10^9 K develops at Eddington accretion rates.

Abstract

We present an extension to the general relativistic radiation magnetohydrodynamic code HARMRAD to account for emission and absorption by thermal cyclo-synchrotron, double Compton, bremsstrahlung, low-temperature OPAL opacities as well as Thomson and Compton scattering. We approximate the radiation field as a Bose-Einstein distribution and evolve it using the radiation number-energy-momentum conservation equations in order to track photon hardening. We perform various simulations to study how these extensions affect the radiative properties of magnetically-arrested disks accreting at Eddington to super-Eddington rates. We find that double Compton dominates bremsstrahlung in the disk within a radius of $r\sim 15r_g$ (gravitational radii) at a hundred times the Eddington accretion rate, and within smaller radii at lower accretion rates. Double Compton and cyclo-synchrotron regulate radiation and gas temperatures in the corona, while cyclo-synchrotron regulates temperatures in the jet. Interestingly, as the accretion rate drops to Eddington, an optically thin corona develops whose gas temperature of $T\sim 10^9$K is $\sim 100$ times higher than the disk's black body temperature. Our results show the importance of double Compton and synchrotron in super-Eddington disks, magnetized coronae, and jets.