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From: monikam@physics.unlv.edu
To: gcnews@aoc.nrao.edu
Subject: Low angular momentum accretion flow model of Sgr A* activity

Hi,
I am sending you a new paper about Galactic Center in ps format.

regards,
Monika Moscibrodzka


\documentclass{ragtime} % NO optional arguments are required

\def\apj{ApJ}
\def\mnras{MNRAS}
\def\nat{Nature}
\def\apjl{ApJL}
\def\aap{A\&A}

\begin{document}

\title{Low angular momentum accretion flow model of Sgr A* activity}

\author{Bo\. zena Czerny\at{1}
         Monika Mo\' scibrodzka\at{1}
         Daniel Proga\at{2}
         Tapas K. Das\at{3}
         and Aneta Siemiginowska\at{4}
}
\institute{1}Copernicus Astronomical Center,
         Bartycka~18, 00\,710 Warsaw,
         Poland\\
\institute{2}Department of Physics, University of Nevada,
         Las Vegas, NV 89154, USA\\
\institute{3}Harish Chandra Research Institute, Allahabad-211 019, India
         \\
\institute{4}Harvard-Smithsonian Center for Astrophysics, 60 Garden
Street,
         Cambridge MA 02138, USA\\


\begin{abstract}

  Sgr A* is a source of strongly variable emission in several energy bands. 
It is generally agreed that this emission comes from the material 
surrounding the black hole which is either falling in or flowing out. The 
activity must be driven by accretion but the character of accretion flow in 
this object is an open question. We suggest that the inflow is dominated by 
the relatively low angular momentum material originating in one of the 
nearby group of stars. Such material flows in directly towards the black 
hole up to the distance of order of ten Schwarzschild radii or less, where 
it hits the angular momentum barrier which leads naturally to a flow 
variability. We study both the analytical and the numerical solutions for 
the flow dynamics, and we analyze the radiation spectra in both cases using 
the Monte Carlo code to simulate the synchrotron, bremsstrahlung and the 
Compton scattering. Our model roughly reproduces the broad band spectrum of 
Sgr A* and its variability if we allow for a small fraction of energy to be 
converted to non-thermal population of electrons. It is also consistent 
(for a range of viewing angles) with the strong constraints on the amount 
of circumnuclear material imposed by the measurements of the Faraday 
rotation.

\end{abstract}