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From: Sascha Trippe  trippe@mpe.mpg.de 
To: gcnews@aoc.nrao.edu
Subject: submit gcnews.tex MNRAS, Nov 2006, in press

%astro-ph/0611737

\documentclass[useAMS,usenatbib]{mn2e}

\begin{document}


\title[Emission from Sagittarius A*]{A polarised infrared flare from 
Sagittarius A* and the signatures of orbiting plasma hotspots\thanks{Partially 
based on observations at the Very Large Telescope (VLT) of the European 
Southern Observatory (ESO), Chile.}}


\author[S. Trippe et al.]
{
S. Trippe,$^1$\thanks{E-mail: {\tt trippe@mpe.mpg.de}} T. 
Paumard,$^1$\thanks{Present adress: Observatoire de Paris - Section de Meudon, 
5 Place Jules Janssen, F-92195 Meudon Cedex, France}  T. Ott,$^1$ S. 
Gillessen,$^1$ F. Eisenhauer,$^1$ F. Martins$^1$ and R. Genzel$^{1,2}$
\\
\\
$^1$Max-Planck-Institut f\"ur extraterrestrische Physik, Postfach 1312, 
D-85741 Garching, Germany \\
$^2$Department of Physics, University of California, CA 94720, Berkeley, USA
}


\date{ Accepted 2006 November 23. Received 2006 November 22; in original form 
2006 September 22 }


\maketitle


\begin{abstract}
In this article we summarise and discuss the infrared, radio, and X-ray 
emission from the supermassive black hole in the Galactic Centre, SgrA*. We 
include new results from near-infrared polarimetric imaging observations 
obtained on May 31st, 2006. In that night, a strong flare in $K_s$ band (2.08 
$\mu$m) reaching top fluxes of $\sim$16 mJy could be observed. This flare was 
highly polarised  (up to $\sim$40 \%) and showed clear sub-structure on a time 
scale of 15 minutes, including a swing in the polarisation angle of about 70 
degrees. For the first time we were able to observe both polarised flux and 
short-time variability, with high significance in the same flare event. This 
result adds decisive information to the puzzle of the SgrA* activity. The 
observed polarisation angle during the flare peak is the same as observed in 
two events in 2004 and 2005. Our observations strongly support the dynamical 
emission model of a decaying plasma hotspot orbiting SgrA* on a relativistic 
orbit. The observed polarisation parameters and their variability with time 
might allow to constrain the orientation of accretion disc and spin axis with 
respect to the Galaxy.
\end{abstract}


\begin{keywords}
Galaxy: centre -- black hole physics -- accretion, accretion discs
\end{keywords}



\end{document}