------------------------------------------------------------------------
From: Farhad Zadeh  zadeh@northwestern.edu 
To: gcnews@aoc.nrao.edu
Subject: submit abstract.tex (Thanks)

\documentclass{article}

\title{     Flaring Activity of Sgr A* at 43 and 22 GHz: Evidence for
            Expanding Hot Plasma}
\author{ F. Yusef-Zadeh, D. Roberts, M. Wardle,
            C. O. Heinke, G. C. Bower}
%astro-ph/0603685

\begin{abstract} We have carried out Very Large Array (VLA) continuum 
observations to 
study the variability of Sgr A* at 43 GHz ($\lambda$=7mm) and 22 GHz 
($\lambda$=13mm). A low level of flare activity has been detected with a 
duration of $\sim$ 2 hours at these frequencies, showing the peak flare 
emission at 43 GHz leading the 22 GHz peak flare by $\sim20$ to 40 minutes. 
The overall characteristics of the flare emission are interpreted in terms of 
the plasmon model of Van der Laan (1966) by considering the ejection and 
adiabatically expansion of a uniform, spherical plasma blob due to flare 
activity. The observed peak of the flare emission with a spectral index 
$\nu^{-\alpha}$ of $\alpha$=1.6 is consistent with the prediction that the 
peak emission shifts toward lower frequencies in an adiabatically-expanding 
self-absorbed source.  We present the expected synchrotron light curves for an 
expanding blob as well as the peak frequency emission as a function of the 
energy spectral index constrained by the available flaring measurements in 
near-IR, sub-millimeter, millimeter and radio wavelengths. We note that the 
blob model is consistent with the available measurements, however, we can not 
rule out the jet model of Sgr A*. If expanding material leaves the 
gravitational potential of Sgr A*, the total mass-loss rate of nonthermal and 
thermal particles is estimated to be $\le 
2\times10^{-8}$\,M$_\odot$\,yr$^{-1}$. We discuss the implication of the 
mass-loss rate since this value matches closely with the estimated accretion 
rate based on polarization measurements.
\end{abstract}
------------------------------------------------------------------------