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From: Monika Moscibrodzka  mmosc@camk.edu.pl 
To: GCNEWS newsletter <gcnews@aoc.nrao.edu>
Subject: submit mmosc.tex, astro-ph/0604516


\documentclass{letter}
\begin{document}

{\title The pattern of accretion flow onto Sgr A*}

%astro-ph/0604516

\author{ Monika Mo\' scibrodzka$^1$, Tapas K. Das$^2$, Bozena 
Czerny$^1$}
\affil{ $^1$N. Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, 
Poland\\
  $^2$ Harish Chandra Research Institute, Allahabad 211 019, India\\
mmosc@camk.edu.pl, tapas@mri.ernet.in, bcz@camk.edu.pl
}

\begin{abstract}

The material accreting onto Sgr A* most probably comes from the nearby stars.
We analyze the pattern of this flow at distances of a fraction of a parsec and 
we argue that the net angular momentum
of this material is low but non-negligible, and the initially supersonic disk
accretion changes into subsonic flow with constant angular momentum. Next we 
estimate the flow parameters
at a distance $R_{BHL}$ from the black hole and we argue that for the 
plausible
  parameter
range the accretion flow is non-stationary. The inflow becomes supersonic at
distance of $\sim 10^4 R_g$ but the solution does not continue below the 
horizon and
the material piles up forming a torus, or a ring, at a distance of
a few up to tens of Schwarzchild radii. Such a torus is known to be unstable
and may explain strong variability of the flow in Sgr A*. Our considerations
show that the temporary formation of such a torus seems to be unavoidable.
  Our best fitting model predicts a rather large accretion
rate of around $4 \cdot 10^{-6}$ $M_{\odot}/ yr$ directly on Sgr A*. We argue 
that
magnetic fields in the flow are tangled and this allows our model to overcome
the disagreement with the Faraday rotation limits.


\end{abstract}

\end{document}