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From: Avery Broderick  abroderick@cfa.harvard.edu 
To: gcnews@aoc.nrao.edu
Subject: sgrA_hotspot.tex MNRAS, submitted

%astro-ph/0509237

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\begin{document}

\title{Imaging
  Optically-Thin Hot Spots Near the Black Hole Horizon of Sgr A* at
  Radio and Near Infrared Wavelengths}
\author{Avery E. Broderick \& Abraham Loeb}
\inst{Institute for Theory and
Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden St.,
MS 51, Cambridge, MA 02138, USA}

\begin{abstract}
Sub milli-arcsecond astrometry and imaging of the black hole Sgr A* at
the Galactic centre may become possible in the near future at infrared
and sub-millimetre wavelengths.  Motivated by observations of short-term
infrared and X-ray variability of \SgrA, in a previous paper we computed
the expected images and light curves, including polarization, associated
with an compact emission region orbiting the central black hole.
We extend this work, using a more realistic hot-spot model and including
the effects of opacity in the underlying accretion flow.  We find that
at infrared wavelengths the qualitative features identified by our
earlier work are present, namely it is possible to extract the
black hole mass and spin from spot images and light curves of the
observed flux and polarization.  At radio wavelengths, disk opacity
produces significant departures from the infrared behaviour, but there
are still generic signatures of the black hole properties.  Detailed
comparison of these results with future data can be used to test general
relativity and to improve existing models for the accretion flow in the
immediate vicinity of the black hole.
\end{abstract}

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