### Résumé du preprint DAPNIA-05-461

DAPNIA-05-461
Repeated X-ray Flaring Activity in Sagittarius A*
G.Belanger, A.Goldwrum, F.Melia, P.Ferrando, N.Grosso, D.Proquet, R.Warwick, F.Yusef-Zadeh
Investigating the spectral and temporal characteristics of the \\xrays coming from
Sagittarius A* (\\sgra) is essential to our development of a more complete understanding
of the emission mechanisms in this supermassive black hole located at the center of
our Galaxy.  Several \\xray flares with varying durations and spectral features have
already been observed from this object.
Here we present the results of two long \\xmm observations of the Galactic nucleus carried
out in 2004, for a total exposure time of nearly 500\\un{ks}.  During these observations we
detected two flares from \\sgra with peak 2--10\\un{keV} luminosities about 40 times
($L_{\\rm X}$\\,$\\sim$\\,9\\,$\\times$\\,$10^{34}$ \\ergpersec) above the quiescent
luminosity: one on 2004 March 31 and another on 2004 August 31.
The total duration of the first flare was about 4 ks. The second, simultaneously
detected in the near-IR, lasted about 10 ks.
%The first flare lasted about 2.5 ks and the second about 5\\un{ks}.
The combined fit on the \\epic spectra yield photon indeces of about 1.5 and 1.9 for
the first and second flare respectively. This hard photon index strongly suggests
the presence of an important population of non-thermal electrons during the event
and supports the view that the majority of flaring events tend to be hard and not very luminous.