The compact radio source Sgr A ^ { * } 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 2001 September 4 .
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 and can be described by simple power law of slope \approx 0.7 .
This XMM-Newton observation confirms the results obtained by Chandra , suggests that , in Sgr A ^ { * } , rapid and intense X-ray flaring is not a rare event and therefore sets some constraints on the emission mechanism models proposed for this source .