  Stellar dynamics indicate the presence of a super massive 3-4x10^6 Msun solm
black hole at the Galactic Center. It is associated with the variable radio,
near-infrared, and X-ray counterpart Sagittarius A* (SgrA*). The goal is the
investigation and understanding of the physical processes responsible for the
variable emission from SgrA*. The observations have been carried out using the
NACO adaptive optics (AO) instrument at the European Southern Observatory's
Very Large Telescope (July 2005, May 2007) and the ACIS-I instrument aboard the
Chandra X-ray Observatory (July 2005). We find that for the July 2005 flare the
variable and polarized NIR emission of SgrA* occurred synchronous with a
moderately bright flare event in the X-ray domain with an excess 2 - 8 keV
luminosity of about 8x10^33erg/s. We find no time lag between the flare events
in the two wavelength bands with a lower limit of less than 10 minutes. The May
2007 flare shows the highest sub-flare to flare contrast observed until now. It
provides evidence for a variation in the profile of consecutive sub-flares. We
confirm that highly variable and NIR polarized flare emission is non-thermal
and that there exists a class of synchronous NIR/X-ray flares. We find that the
flaring state can be explained via the synchrotron self-Compton (SSC) process
involving up-scattered sub-millimeter photons from a compact source component.
The observations can be interpreted in a model involving a temporary disk with
a short jet. In the disk component the flux density variations can be explained
due to spots on relativistic orbits around the central super massive black hole
(SMBH). The profile variations for the May 2007 flare are interpreted as a
variation of the spot structure due to differential rotation within the disk.
