Flares of Sagittarius A* at Short Millimeter Wavelengths

A. Miyazaki1, T. Tsutsumi 2, M. Tsuboi 3

1 Nobeyama Radio Observatory, Japan
2 Harvard-Smithsonian CfA, USA
3 Institute of Astrophysics and Planetary Science, Ibaraki University, Japan

E-mail contact: amiya@nro.nao.ac.jp

We have performed intensity monitoring observations toward the Galactic center compact nonthermal radio source, Sgr A*, at = 3mm and 2 mm (100 and 140 GHz) from 1996 to 2002 using the Nobeyama Millimeter Array (NMA). In 1996, 1997, 1998, and 2000, the observations were performed during a period of one to two months for each years in a single (intermediate resolution) array configuration in order to exclude a systematic error caused by sampling different source structures with the different beam sizes. From November 2000 to May 2001, and November 2001 to May 2002, the observations were carried out over several months in order to investigate the longer term variability. At the GC workshop 1998, we reported a flare observed in March 1998 (Tsuboi et al. 1999). In addition to the flare, we detected two more flares in March 2000 and April 2002. The peak flux densities of the flares were 2-3 Jy at 3 mm, while the mean quiescent flux densities was ~1 Jy. In particular to the March 2000 flare, the flux densities of Sgr A* at 3 mm had reached 2 peaks (~3 Jy) on 7 and 21 March and increased delta S/ S ~ 200% for both. This flare phase had continued for a month and shows more complex activity. On the other hand, maximum flux density at 2 mm was 4 Jy in 8 March 2000 and the flux was decreased to half in a day. We folded the NMA light curve with a quasi-period of 106 days determined from the analysis of the VLA centimeter wavelength data by Zhao, Bower and Goss (2001). The folded lightcurve shows distinct high and low activity states.