Flare emission from Sagittarius A*
  Based on Bremer et al. (2011) and Eckart et al. (2012) we report on
simultaneous observations and modeling of the millimeter, near-infrared, and
X-ray flare emission of the source Sagittarius A* (SgrA*) associated with the
super-massive black hole at the Galactic Center. We study physical processes
giving rise to the variable emission of SgrA* from the radio to the X-ray
domain. To explain the statistics of the observed variability of the (sub-)mm
spectrum of SgrA*, we use a sample of simultaneous NIR/X-ray flare peaks and
model the flares using a synchrotron and SSC mechanism. The observations reveal
flaring activity in all wavelength bands that can be modeled as the signal from
adiabatically expanding synchrotron self-Compton (SSC) components. The model
parameters suggest that either the adiabatically expanding source components
have a bulk motion larger than v_exp or the expanding material contributes to a
corona or disk, confined to the immediate surroundings of SgrA*. For the bulk
of the synchrotron and SSC models, we find synchrotron turnover frequencies in
the range 300-400 GHz. For the pure synchrotron models this results in
densities of relativistic particles of the order of 10^6.5 cm^-3 and for the
SSC models, the median densities are about one order of magnitude higher.
However, to obtain a realistic description of the frequency-dependent
variability amplitude of SgrA*, models with higher turnover frequencies and
even higher densities are required. We discuss the results in the framework of
possible deviations from equilibrium between particle and magnetic field
energy. We also summarize alternative models to explain the broad-band
variability of SgrA*.
