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First-principle modeling of a black-hole corona

Presentation #406.05 in the session Stellar & Compact Objects III.

Published onJul 01, 2023
First-principle modeling of a black-hole corona

Black-hole X-ray binaries and active galactic nuclei both emit hard non-thermal X-rays, which cannot be explained by pure thermal emission from an accretion disk. This indicates the presence of a “coronal” hot, optically thin plasma in the vicinity of the disk, which is able to upscatter thermal photons. However, both its geometry and physical properties are still poorly understood. To explain both the fast inverse Compton cooling and the high luminosity of the corona, it is often assumed that coronae are magnetically dominated, the primary energy source being fast magnetic reconnection. In this regime, it is necessary to include kinetic physics to capture the correct dissipation rate. Recently, X-ray polarimetric observations of Cyg X-1 by the IXPE collaboration have indicated that this corona, though compact, must be laterally extended along the disk. Therefore, global effects must also be included in a self-consistent modeling of the corona. In this talk, I will present recent efforts in an ab initio modeling of black-hole coronae that capture both of these aspects. We have performed global axisymmetric general-relativistic kinetic simulations of the coronal plasma located above a thin accretion disk. We inject magnetic loops at the disk surface, which are then sheared and shaken by flows within the disk, driving magnetic reconnection between the loops. We have quantified the amount of dissipation for various loop geometries and Compton cooling strengths, as well as resulting electron spectra. These simulations support magnetic reconnection as the source of hard X-ray emission in black-hole coronae.

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