Flux monitoring of Sagittarius A* at mm-wavelengths

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We performed the monitoring observations of the fbx density toward the Galactic center compact radio source, Sagittarius A* (Sgr A*), which is associated with a supermassive black hole, since 1996 using the Nobeyama Millimeter Array (NMA). The monitoring observations of Sgr A* were carried out in the 3- and 2-mm (100 and 140 GHz) bands over one to several months on each NMA observable season. We have detected several fares of Sgr A * with duration of, roughly, one month. The fbx density at the fare peak increases 100%–200% at 100 GHz band and 200%–400% at 140 GHz band, respectively, while the averaged quiescent fbx density was about 1 Jy. We also found some intraday variations (IDVs) of Sgr A* at both 2- and 3-mm bands. The shortest twofold increase timescale of the IDV is estimated to be about 1.5 hr at 140 GHz. This short timescale variability suggests that the physical size of emitting region is compact on a scale at or below about 12 AU (∼150 RS). The IDV at mm-wavelengths has a similar increase timescale as those in the X-ray and infrared fares but has a smaller amplitude.