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From: Farhad Zadeh  zadeh@oort.astro.nwu.edu 
To: gcnews@aoc.nrao.edu
Subject: OH survey abstract
MIME-Version: 1.0

%astro-ph/9907370
\title{Three New Supernova Remnant OH Masers Near the Galactic Center: Evidence
  for Large Scale Maser Emission from Supernova Remnants}
 
\author{F. Yusef-Zadeh, W. M. Goss, D. A. Roberts, B. Robinson and D. A. Frail}

\begin{abstract}
A survey of the inner 8$^\circ \times 1^\circ$ of the Galactic plane
toward the Galactic center has been carried out at the 1720 MHz transition
of OH molecule using the VLA in its D configuration with a resolution of
$\approx70''\times45''$. The detection of compact 1720 MHz OH masers
associated with three supernova remnants G357.7+0.3, G1.13--0.1 (Sgr D)
and G1.4--0.1 as well as new extended maser line emission from G357.7+0.3
and G357.7--0.1 (the Tornado Nebula) were then followed up by A-array
observations with spectral and spatial resolutions of 0.3 \kms and
$\approx3''\times2''$, respectively. 

The 1720 MHz OH maser line emission is considered to be a powerful shock
diagnostic and is collisionally pumped by H$_2$ molecules at the site
where C-type supernova shocks drive into adjacent molecular clouds. The
new observations show clear evidence of extended features coincident with
compact and bright masers, the best example of which is a coherent feature
over a scale of about 20 pc surrounding the shell of the SNR G357.7+0.3.
We argue that this remarkable feature is an OH maser and is physically
associated with the remnant. This implies that the ambient molecular cloud
is uniform in its density and temperature with restricted range of pumping
conditions and survives the passage of a large-scale shock front.  
\end{abstract}