Comparison of the ion-to-electron temperature ratio prescription: GRMHD simulations with electron thermodynamics

Abstract

The Event Horizon Telescope (EHT) collaboration, an Earth-size sub-millimetre radio interferometer, recently captured the first images of the central supermassive black hole in M87. These images were interpreted as gravitationally-lensed synchrotron emission from hot plasma orbiting around the black hole. In the accretion flows around low-luminosity active galactic nuclei such as M87, electrons and ions are not in thermal equilibrium. Therefore, the electron temperature, which is important for the thermal synchrotron radiation at EHT frequencies of 230 GHz, is not independently determined. In this work, we investigate the commonly used parameterised ion-to-electron temperature ratio prescription, the so-called R-$\beta$ model, considering images at 230 GHz by comparing with electron-heating prescriptions obtained from general-relativistic magnetohydrodynamical (GRMHD) simulations of magnetised accretion flows in a Magnetically Arrested Disc (MAD) regime with different recipes for the electron thermodynamics. When comparing images at 230 GHz, we find a very good match between images produced with the R-$\beta$ prescription and those produced with the turbulent- and magnetic reconnection- heating prescriptions. Indeed, this match is on average even better than that obtained when comparing the set of images built with the R-$\beta$ prescription with either a randomly chosen image or with a time-averaged one. From this comparative study of different physical aspects, which include the image, visibilities, broadband spectra, and light curves, we conclude that, within the context of images at 230 GHz relative to MAD accretion flows around supermassive black holes, the commonly-used and simple R-$\beta$ model is able to reproduce well the various and more complex electron-heating prescriptions considered here.

18 pages, 22 figures, accepted for publication in MNRAS

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• Dynamics and Emission Properties of Flux Ropes from Two-Temperature GRMHD Simulations with Multiple Magnetic Loops
• Truncated accretion discs in black hole X-ray binaries: dynamics and variability signatures
• Impacts of nonthermal emission on the images of a black hole shadow and extended jets in two-temperature GRMHD simulations
• Illuminating Black Hole Shadow with Dark Matter Annihilation
• Deep learning inference with the Event Horizon Telescope II. The Zingularity framework for Bayesian artificial neural networks
• Impact of the nonthermal electron radiation effects on the horizon scale image structure of Sagittarius A*
• Forgotten treasures in the HST/FOC UV imaging polarimetric archives of active galactic nuclei III. Five years monitoring of M87
• Global resistive MHD accretion flows around spinning AGNs: impact of resistivity on MAD state
• Non-thermal Synchrotron Emission and Polarization Signatures during Black Hole Flux Eruptions
• Radiative Cooling Effects on Plasmoid Formation in Black Hole Accretion Flows with Multiple Magnetic Loops
• Impacts of radiative cooling on the images of a black hole shadow and extended jets in two-temperature GRMHD simulations
• DoG-HiT: A novel VLBI Multiscale Imaging Approach
• Investigating the Disk-Jet Structure in M87 through Flux Separation in the Linear and Circular Polarization Images
• The role of the thermal properties of electrons on the dispersion properties of Alfvén waves in space plasmas
• Impact of non-thermal particles on the spectral and structural properties of M87