Observational appearances of isolated stellar-mass black hole accretion - theory and observations

TL;DR

This paper explores the theoretical properties and observational signatures of accretion onto isolated stellar-mass black holes, emphasizing magnetic effects and nonthermal emissions, supported by high-resolution optical observations of candidate black holes.

Contribution

It introduces a model accounting for magnetic adiabatic invariants and reconnection effects, predicting nonthermal emission components in black hole accretion flows.

Findings

Magnetic fields increase adiabatic heating efficiency by 25%.

Reconnection events produce significant nonthermal electron populations.

Optical observations of candidates support the model's predictions.

Abstract

General properties of accretion onto isolated stellar mass black holes in the Galaxy are discussed. An analysis of plasma internal energy growth during the infall is performed. Adiabatic heating of collisionless accretion flow due to magnetic adiabatic invariant conservation is 25% more efficient than in the standard non-magnetized gas case. It is shown that magnetic field line reconnections in discrete current sheets lead to significant nonthermal electron component formation, which leads to a formation of a hard (UV, X-ray, up to gamma), highly variable spectral component in addition to the standard synchrotron optical component first derived by Shvartsman generated by thermal electrons in the magnetic field of the accretion flow. Properties of accretion flow emission variability are discussed. Observation results of two single black hole candidates - gravitational lens MACHO-1999-BLG-22 and radio-loud x-ray source with featureless optical spectrum J1942+10 - in optical band with high temporal resolution are presented and interpreted in the framework of the proposed model.