Flaring Activity of Sgr A*: Expanding Hot Blobs

Kavli Institute for Astrophysics and Space Research, MIT, Cambridge, MA 02139-4307E-mail:fkb@space.mit.eduSgr A* is considered to be a massive black hole at the Galactic center and is known to be variablein radio, millimeter, near-IR and X-rays. Recent multi-wavelength observing campaigns show asimultaneous X-ray and near-IR flare, as well as sub-millimeter and near-IR flares from Sgr A*.The flare activity is thought to be arising from the innermost region of Sgr A*. We have recentlyargued that the duration of flares in near-IR and submillimeter wavelengths implies that the burstof emission expands and cools on a dynamical time scale before the flares leave Sgr A*. Thedetection of radio flares with a time delay in the range of 20 an d 40 minutes between 7 and 12mmpeak emission implies adiabatic expansion of a uniform, spherical hot blob due to flare activity.We suspect that this simple outflow picture shows some of the c haracteristics that are known totake place in microquasars, thus we may learn much from comparative study of Sgr A* and itsenvironment vs. microquasars.VI Microquasar Workshop: Microquasars and BeyondSeptember 18-22 2006Societa del Casino, Como, Italy