Variability of Sagittarius A*: Flares at 1 millimeter

We report the results from recent observations of Sgr A* at short-/submillimeter wavelengths made with the partially finished Submillimeter Array (SMA) on Mauna Kea. A total of 25 epochs of observations were carried out over the past 15 months from 2001 March to 2002 May. Noticeable variations in flux density at 1.3 mm were observed showing three flares. The SMA observations suggest that Sgr A* highly increases toward submillimeter wavelengths during a flare, suggesting the presence of a break wavelength in spectral index around 3 mm. A cross-correlation of the SMA data at 1 mm with the Very Large Array data at 1 cm shows a global delay of t(delay) > delay 3 days, suggesting that submillimeter wavelengths tend to peak first. Only marginal day-to-day variations in flux density (2- 3 sigma) have been detected at 1.3 mm. No significant flares on a short timescale (similar to1 hr) have been observed at 1.3 mm. We also failed to detect significant periodic signals at a level of 5% (3 sigma) from Sgr A* in a periodic searching window ranging from 10 minutes to 2.5 hr. The flares observed at the wavelengths between short-centimeter and submillimeter might be a result of collective mass ejections associated with X-ray flares that originate from the inner region of the accretion disk near the supermassive black hole.