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From: Farhad Zadeh  zadeh@northwestern.edu 
To: gcnews@aoc.nrao.edu

%astro-ph/0612156

\title{Flaring Activity of Sgr A*: Expanding Hot Blobs}

\authors{F. Yusef-Zadeh, M. Wardle, D. A. Roberts,
C. O. Heinke, C. D. Dowell, W. D. Cotton, G. C. Bower \&
F. K. Baganoff}

\begin{abstract}
Sgr A* is considered to be a massive black hole at the Galactic center and is 
known to be variable in radio, millimeter, near-IR and X-rays. Recent 
multi-wavelength observing campaigns show a simultaneous X-ray and near-IR 
flare, as well as sub-millimeter and near-IR flares from Sgr A*. The flare 
activity is thought to be arising from the innermost region of Sgr A*. We have 
recently argued that the duration of flares in near-IR and submillimeter 
wavelengths implies that the burst of emission expands and cools on a 
dynamical time scale before the flares leave Sgr A*. The detection of radio 
flares with a time delay in the range of 20 and 40 minutes between 7 and 12mm 
peak emission implies adiabatic expansion of a uniform, spherical hot blob due 
to flare activity. We suspect that this simple outflow picture shows some of 
the characteristics that are known to take place in microquasars, thus we may 
learn much from comparative study of Sgr A* and its environment vs. 
microquasars.
\end{abstract}