Variability of Sagittarius A*: Flares at 1 Millimeter

We report the results from recent observations of Sgr A* atshort-/sub-millimeter wavelengths made with the partially finishedSub-Millimeter Array (SMA) on Mauna Kea. A total of 25 epochs of observationswere carried out over the past 15 months in 2001 March to 2002 May. Noticeablevariations in flux density at 1.3 mm were observed showing three ``flares''.The SMA observations suggest that Sgr A* highly increases towards submillimeterwavelengths during a flare suggesting the presence of a break wavelength inspectral index around 3 mm. A cross-correlation of the SMA data at 1 mm withthe VLA data at 1 cm show a global delay of $t_{delay} > 3d$, suggesting thatsub-millimeter wavelengths tend to peak first. Only marginal day-to-dayvariations in flux density (2-3 $\sigma$) have been detected at 1.3 mm. Nosignificant flares on a short time scale ($\sim1$ hr) have been observed at 1.3mm. 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 min to2.5 hr. The flares observed at the wavelengths between short-centimeter andsub-millimeter might be a result of collective mass ejections associated withX-ray flares that originate from the inner region of the accretion disk nearthe supermassive black hole.Comment: 9 pages including 4 figures (eps). Prepared using AASTeX v5.0 LaTeX 2e macros. to appear in the Astrophysical Journal Lette