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From: Fulvio Melia  melia@physics.arizona.edu 
To: hfalcke@mpifr-bonn.mpg.de


\title{Electron-positron Annihilation Radiation\\
       from Sgr A East at the Galactic Center}

\author{Marco Fatuzzo$^{1,2}$, Fulvio Melia$^{2,3,}$\altaffilmark{4}, and
Johann Rafelski$^2$}
\affil{$^1$Physics Department, Xavier University, Cincinnati, OH  45207}
\affil{$^2$Physics Department, The University of Arizona, Tucson, AZ 85721}
\affil{$^3$Steward Observatory, The University of Arizona, Tucson, AZ 85721}
\altaffiltext{4}{Sir Thomas Lyle Fellow and Miegunyah Fellow.}

\begin{abstract}
Maps of the Galactic electron-positron annihilation radiation show
evidence for three distinct and significant features: (1) a central
bulge source, (2) emission in the Galactic plane, and (3) an
enhancement of emission at positive latitudes above the Galactic
Center.  In this paper, we explore the possibility that Sgr A East,
a very prominent radio structure surrounding the Galactic nucleus,
may be a significant contributer to the
central bulge feature.  The motivation for doing so stems
from a recently proposed link between this radio object and the EGRET
$\gamma$-ray source 2EG J1746-2852. If this association is correct, then Sgr A 
East
is also expected to be a source of copious positron production.  The results 
presented
here show that indeed Sgr A East must have produced a numerically significant
population of positrons, but also that most of them have not yet had
sufficient time to thermalize and annihilate.  As such, Sgr A East
by itself does not appear to be the dominant {\it current} source of
annihilation radiation, but it will be when the positrons have
cooled sufficiently and they have become thermalized.  This raises the 
interesting possibility that the bulge component may be due to the
relics of earlier explosive events like the one that produced Sgr A East.
\end{abstract}




                  Fulvio Melia
            The University of Arizona             
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  |Department of Physics & Steward Observatory|
  |      Rm 447, PAS #81   (520) 621-9651     | 
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      http://www.physics.arizona.edu/~melia        



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