X-ray Flares and Quiescent Emission of Sgr A* from Chandra Observations

Frederick K. Baganoff

1 Center for Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

E-mail contact: fkb@space.mit.edu

Sgr A* was observed with the ACIS-I instrument on the Chandra X-Ray Observatory for 0.5 Ms during the period 22 May 2002 to 4 June 2002. Three X-ray flares with amplitudes in excess of a factor of 10 and 4 or 5 flares of lower amplitude were detected. The flare durations ranged from half an hour to several hours with rise and fall times of a few hundred seconds, similar to the original X-ray flare discovered with Chandra in 2000. These observations confirm that rapid and intense X-ray flaring of Sgr A* is common. Averaging over all Chandra observations from 1999-2002, a total of 0.6 Ms, the mean rate is 1.2 +/- 0.4 flares per day. The Chandra observations in late May and early June 2002 were part of a week-long campaign including major ground-based telescopes to monitor Sgr A* simultaneously for varying amounts of time in the X-ray, infrared, millimeter, and radio wavebands. Here I present the results of spectral, spatial, and timing analyses of the X-ray emission of Sgr A* in the quiescent and flaring states. The results of the multiwavelength campaign are summarized briefly. The detailed results of the campaign are presented by Baganoff et al. elsewhere in this workshop. Existing models for the accretion flow and emission mechanisms are evaluated in light of these new results.