Occultation of the Quiescent Emission from Sgr A* by IR Flares
  We have investigated the nature of flare emission from Sgr A* during
multi-wavelength observations of this source that took place in 2004, 2005 and
2006. We present evidence for dimming of submm and radio flux during the peak
of near-IR flares. This suggests that the variability of Sgr A* across its
wavelength spectrum is phenomenologically related. The model explaining this
new behavior of flare activity could be consistent with adiabatically cooling
plasma blobs that are expanding but also partially eclipsing the background
quiescent emission from Sgr A*. When a flare is launched, the plasma blob is
most compact and is brightest in the optically thin regime whereas the emission
in radio/submm wavelengths has a higher opacity. Absorption in the observed
light curve of Sgr A* at radio/submm flux is due to the combined effects of
lower brightness temperature of plasma blobs with respect to the quiescent
brightness temperature and high opacity of plasma blobs. This implies that
plasma blobs are mainly placed in the magnetosphere of a disk-like flow or
further out in the flow. The depth of the absorption being larger in submm than
in radio wavelengths implies that the intrinsic size of the quiescent emission
increases with increasing wavelength which is consistent with previous size
measurements of Sgr A*. Lastly, we believe that occultation of the quiescent
emission of Sgr A* at radio/submm by IR flares can be used as a powerful tool
to identify flare activity at its earliest phase of its evolution.
