------------------------------------------------------------------------
From: Siming Liu  liusm@stanford.edu 
To: gcnews@zia.aoc.nrao.edu
Subject: submit ms.tex ApJL, July 2004, in press.

%astro-ph/0403487


\documentclass[12pt,preprint]{aastex}

\newcommand{\myemail}{liusm@stanford.edu}


\shorttitle{Electron Acceleration in Sgr A*}

\begin{document}

\title{Electron Acceleration around the Supermassive Black Hole at the 
Galactic Center}


\author{Siming Liu\altaffilmark{1}, Vah\'{e} Petrosian\altaffilmark{2} and
Fulvio Melia\altaffilmark{3}}
of Physics, Stanford
University, Stanford,
CA 94305}
\altaffiltext{3}{Physics Department and Steward Observatory, The 
University of Arizona,
Tucson, AZ 85721; Sir Thomas Lyle Fellow and Miegunyah Fellow.}

\begin{abstract}

The recent detection of variable infrared emission from Sagittarius A*, 
combined with its
previously observed flare activity in X-rays, provides compelling 
evidence that at least a
portion of this object's emission is produced by nonthermal electrons.  
The polarization
and variability of Sgr A*'s emission depend strongly on the observed 
wavelength,
indicating distinct physical processes.  We show here that acceleration 
of electrons by
plasma wave turbulence in hot gases near the black hole's event horizon, 
though with
several theoretical uncertainties, can reasonably account both for Sgr 
A*'s mm
and shorter wavelength emission in the quiescent state, and for the 
infrared and X-ray
flares, induced either via an enhancement of the mass accretion rate 
onto the black hole or
by reorganization of magnetic fields coupled to the accretion gas. 
High-energy electrons
diffusing away from the acceleration site toward larger radii might 
account for
Sgr A*'s emission at longer wavelengths. The acceleration model produces 
prominent
IR flares accompanying X-ray bursts. Future coordinated multi-wavelength 
observations will
be able to test this model and constrain its parameters.

\end{abstract}