2004ApJ...611L..97M

We have performed the monitoring observations of the flux density of Sagittarius A* at short millimeter wavelengths (100 and 140 GHz bands) for 7 years in the period from 1996 to 2003 using the Nobeyama Millimeter Array. We found intraday variation of Sgr A* in the 2000 March flare. The flux density at the peak of the flares increases 100%-200% at 100 GHz and 200%-400% at 140 GHz (ΔS/S), respectively. The twofold increase timescale of the flare is estimated to be about 1.5 hr at 140 GHz. The intraday variation at millimeter wavelengths has a similar increase timescale as those in the X-ray and infrared flares but has smaller amplitude. This short timescale variability suggests that the physical size of the emitting region is smaller than 12 AU (~150R_S). The decay timescale of the flare was at most 24 hr. Such a light curve with rapid increase and slow decay is similar to that often observed in outburst phenomena with ejections.