Make Reconnection Cool Again

Alicia Savelli (University of Toronto)

July 09, 2025

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Abstract: Magnetic reconnection in astrophysical phenomena often occurs in the radiative regime in the relativistic limit, relevant to emission observed from astrophysical objects such as black hole coronae, flares from magnetically arrested disks, pulsars, and magnetars. For black hole coronae in particular, relativistic radiative reconnection is thought to power the background X-ray emission through Inverse Compton scattering on seed photons by the bulk flow. We model this process both with kinetic theory — describing the effects of energy-momentum loss due to scattering as a radiative drag force, and with fluid theory — describing the same effect as a sink term in the energy-momentum conservation equations. I will derive both kinetic and fluid theory cooling terms and their scaling, and show for the first time that the fluid theory analytics recovers kinetic radiative reconnection in charge-starved X-points. Such a mapping finally provides a physically informed subgrid model for relativistic radiative reconnection in magnetohydrodynamic simulations of black hole accretion disk coronae.