Journal Article

Low angular momentum flow model II for Sgr A*

T. Okuda

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 441, issue 3, pages 2354-2360
ISSN: 0035-8711
Published online May 2014 | e-ISSN: 1365-2966 | DOI:
Low angular momentum flow model II for Sgr A*

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We examine 1D two-temperature accretion flows around a supermassive black hole, adopting the specific angular momentum λ, the total specific energy ϵ and the input accretion rate Ṁinput = 4.0 × 10−6 M yr−1 estimated in the recent analysis of stellar wind of nearby stars around Sgr A*. The two-temperature flow is almost adiabatic even if we take account of the heating of electrons by ions, the bremsstrahlung cooling and the synchrotron cooling, as long as the ratio β of the magnetic energy density to the thermal energy density is taken to be as β ≤ 1. The different temperatures of ions and electrons are caused by the different adiabatic indices of ions and electrons which depend on their temperature states under the relativistic regime. The total luminosity increases with increasing β and results in ∼1035–1036 erg s−1 for β = 10−3–1. Furthermore, from 2D time-dependent hydrodynamical calculations of the above flow, we find that the irregularly oscillating shocks are formed in the inner region and that the luminosity and the mass-outflow rate vary by a factor of 2–3 and 1.5–4, respectively. The time variability may be relevant to the flare activity of Sgr A*.

Keywords: accretion, accretion discs; black hole physics; hydrodynamics; radiation mechanisms: thermal; shock waves; Galaxy: centre

Journal Article.  5090 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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