Volume 440, Number 1, September II 2005
|Page(s)||223 - 238|
|Section||Stellar structure and evolution|
|Published online||19 August 2005|
Low-rate accretion onto isolated stellar-mass black holes
Special Astrophysical Observatory, Nizhnij Arkhyz, Karachaevo-Cherkesia 369167, Russia e-mail: email@example.com
2 Isaac Newton Institute of Chile, SAO Branch, Russia
Accepted: 28 April 2005
Magnetic field behaviour in a spherically-symmetric accretion flow for parameters typical of single black holes in the Galaxy is discussed. It is shown that in the majority of Galaxy volume, accretion onto single stellar-mass black holes will be spherical and have a low accretion rate ( of the Eddington rate). 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 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. In a framework of quasi-diffusion acceleration, the “energy-radius” electron distribution is computed and the function describing the shape of synchrotron radiation spectrum is constructed. It is shown that nonthermal electron emission leads to 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 accretion flow. For typical interstellar medium parameters, a black hole at 100 pc distance will be a 16–25m optical source coinciding with the highly variable bright X-ray counterpart, while the variable component of optical emission will be about 18–27m. The typical time scale of the variability is 10-4 s, with relative flare amplitudes of 0.2–6% in various spectral bands. Possible applications of these results to the problem of search for single black holes are discussed.
Key words: accretion, accretion disks / magnetic fields
© ESO, 2005
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.