Sgr A* , the massive black hole at the center of the Galaxy , varies in radio through X-ray emission on hourly time scales .
The flare activity is thought to arise from the innermost region of an accretion flow onto Sgr A* .
We present simultaneous light curves of Sgr A* in radio , sub-mm and X-rays that show a possible time delay of 110 \pm 17 minutes between X-ray and 850 \mu m suggesting that the sub-mm flare emission is optically thick .
At radio wavelengths , we detect time lags of of 20.4 \pm 6.8 , 30 \pm 12 and 20 \pm 6 minutes between the flare peaks observed at 13 and 7 mm ( 22 and 43 GHz ) in three different epochs using the VLA .
Linear polarization of 1 \pm 0.2 % and 0.7 \pm 0.1 % is detected at 7 and 13 mm , respectively , when averaged over the entire observation on 2006 July 17 .
A simple model of a bubble of synchrotron emitting electrons cooling via adiabatic expansion can explain the time delay between various wavelengths , the asymmetric shape of the light curves , and the observed polarization of the flare emission at 43 and 22 GHz .
The derived physical quantities that characterize the emission give an expansion speed of v _ { exp } \sim 0.003 - 0.1 c , magnetic field of B \sim 10-70 Gauss and particle spectral index p \sim 1-2 .
These parameters suggest that the associated plasma can not escape from Sgr A* unless it has a large bulk motion .