Letter to the Editor

XMM-Newton observation of the brightest X-ray flare detected so far from Sgr A*

¹ Max-Planck-Institut für extraterrestrische Physik, PO Box 1312, Garching bei München 85741, Germany
² Laboratoire d'Astrophysique de Grenoble, Université Joseph-Fourier, BP 53, 38041 Grenoble Cedex 9, France
³ CEA, DSM, DAPNIA, Service d'Astrophysique, C.E. Saclay, 91191 Gif-Sur-Yvette Cedex, France
⁴ Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK

Corresponding author: D. Porquet, dporquet@mpe.mpg.de

Received: 26 May 2003
Accepted: 26 June 2003

Abstract

We report the high S/N observation on October 3, 2002 with XMM-Newton of the brightest X-ray flare detected so far from Sgr A* with a duration shorter than one hour (~2.7 ks). The light curve is almost symmetrical with respect to the peak flare, and no significant difference between the soft and hard X-ray range is detected. The overall flare spectrum is well represented by an absorbed power-law with a soft photon spectral index of , and a peak 2–10 keV luminosity of 3.6 erg s^-1, i.e. a factor 160 higher than the Sgr A* quiescent value. No significant spectral change during the flare is observed. This X-ray flare is very different from other bright flares reported so far: it is much brighter and softer. The present accurate determination of the flare characteristics challenge the current interpretation of the physical processes occuring inside the very close environment of Sgr A* by bringing very strong constraints for the theoretical flare models.