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 sgraxmm.tex ApJ Lett, Jul 2002, submitted
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%astro-ph/0207620

% Version 24/07/2002 submitted to ApJ Lett
%
\documentclass[12pt,preprint]{aastex}

\newcommand{\sgra}    {\mbox{\rm\,Sgr~A$^*$}}

\slugcomment{Version 24/07/02: submitted to the editor of ApJ Letters}

\begin{document}

\title{A New X-Ray Flare from the Galactic Nucleus Detected with the XMM-Newton 
Photon Imaging Cameras}

\author{A. Goldwurm, E. Brion\altaffilmark{1}, 
P. Goldoni, P. Ferrando, 
F. Daigne, A. Decourchelle,
}
\affil{
Service d'Astrophysique, DAPNIA/DSM/CEA, CE-Saclay, F-91191 Gif-Sur-Yvette, 
France}
%\email{agoldwurm@cea.fr}
\author{R.S.~Warwick,}
\affil{
Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, 
UK}
\author{P. Predehl}
\affil{
Max-Planck Institut f\"{u}r Extraterrestrische Physik, Postfach 1312, 85741 
Garching, Germany}

\altaffiltext{1}{Astronomical Observatory and University ``Louis Pasteur'',
Strasbourg, France}

\begin{abstract}

\sgra, the compact radio source, believed to be the counterpart 
of the massive black hole at the galactic nucleus, 
was observed to undergo rapid and intense flaring activity in X-rays 
with Chandra in October 2000. 
We report here the detection with XMM-Newton EPIC cameras 
of the early phase of a similar X-ray flare from this source, 
which occurred on September 4, 2001.
The source 2-10 keV luminosity increased by a factor $\approx$~20 
to reach a level of 4~10$^{34}$~erg~s$^{-1}$ in a time interval 
of about 900~s, just before the end of the observation.
The data indicate that the source spectrum was hard 
during the flare.
This XMM-Newton observation confirms the results obtained by Chandra and 
suggests that, in \sgra, rapid and intense X-ray flaring is not a rare event.
This can constrain the emission mechanism models proposed for this 
source, 
and also implies that the crucial multiwavelength observation 
programs planned to explore the behaviour of the radio/sub-mm and
hard X-ray/gamma-ray emissions during the X-ray flares, 
have a good chance of success.

\end{abstract}

\keywords{accretion -- black hole physics -- Galaxy:
center}



*************************************************
Andrea Goldwurm
Service d'Astrophysique / CEA-Saclay
Centre d'Etudes de Saclay 
Orme des Merisiers - Bat. 709
91191 - Gif sur Yvette   Cedex 
France
Tel:    +33 (0)1 69 08 27 92  /  (0)1 69 08 80 49
Fax:    +33 (0)1 69 08 65 77
E-mail: agoldwurm@cea.fr
*************************************************