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F.K. Baganoff (MIT)
Sgr A*, the supermassive black hole at the center of the Milky Way, has been the target of a series of pointed observations with the ACIS-I instrument on the Chandra X-ray Observatory. The bulk of the data come from a 0.5-Ms exposure during the period 22 May 2002 to 4 June 2002. This extended observation detected three X-ray flares with amplitudes in excess of a factor of 10 and several flares by more than a factor of 5. 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 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 of factor-of-10 flares is 0.6 +/- 0.3 per day. During the Chandra observations, a network of ground-based telescopes were employed for simultaneous observations: the Keck-I Telescope at 2 and 10 microns; the VLT at 2 to 5 microns; the Magellan-Baade Telescope at 10 microns; the SMA at 1 mm; the ATCA and the Owens Valley Millimeter Array at 3 mm; the VLBA at 7 mm; and the VLA at 0.7, 1.3 and 2 cm. Contrary to most theoretical predictions, the X-ray flares were not accompanied by large variations at the longer wavelengths. There may be some evidence for mm variations at a few tens of percent level; the current upper limits are about 50%. The quiescent X-ray emission within 1.5 arcsec of Sgr A* shows a strong emission line from highly ionized iron and is resolved by Chandra on a scale consistent with the Bondi capture radius for the black hole. This research was supported by NASA grant NAS8-39073.
Bulletin of the American Astronomical Society,
35#2
© 2003. The American Astronomical Soceity.