Impact of non-thermal electron radiation effects on the horizon scale image structure of Sagittarius A∗

Abstract

ABSTRACT The Event Horizon Telescope (EHT), with ∼20 $\mu$ as high angular resolution, recently resolved the millimetre image of the suppermassive black hole in the Galaxy, Sagittarius A∗. This opens a new window to study the plasma on horizon scales. The accreting disc probably contains a small fraction of non-thermal electrons and their emissions should contribute to the observed image. We study if such contributions are sufficient to cause structural differences detectable by current and future observational capabilities. We introduce non-thermal electrons in a semi-analytical accretion disc, which considers viscosity-leading heating processes, and adopt a continued hybrid electron energy distribution of thermal distribution and power-law tail. We generate the black hole images and extract the structural features as crescent parameters. We find the existence of non-thermal electron radiation makes the crescent much brighter, slightly larger, moderately thicker, and much more symmetric. When the non-thermal connecting Lorentz factor γc = 65, which is equivalent to the non-thermal electrons accounting for ∼1.5 per cent of the totals, non-thermal effects cause ∼2 per cent size difference at 230 GHz. Comparing with the structural changes caused by other physical factors, including inclination between the system and the observer, black hole spin, and interstellar medium scattering effects, we find that although non-thermal electron radiation takes the most unimportant role at 230 GHz, it becomes more significant at 345 GHz.