Multi-Wavelength Study of Sgr A*: The Short Time Scale Variability
  To understand the correlation and the radiation mechanism of flare emission
in different wavelength bands, we have coordinated a number of telescopes to
observe SgrA* simultaneously. We focus only on one aspect of the preliminary
results of our multi-wavelength observing campaigns, namely, the short time
scale variability of emission from SgrA* in near-IR, X-ray and radio
wavelengths. The structure function analysis indicate most of the power
spectral density is detected on hourly time scales in all wavelength bands. We
also report minute time scale variability at 7 and 13mm placing a strong
constraint on the nature of the variable emission. The hourly time scale
variability can be explained in the context of a model in which the peak
frequency of emission shifts toward lower frequencies as a self-absorbed
synchrotron source expands adiabatically near the acceleration site. The short
time scale variability, on the other hand, places a strong constraint on the
size of the emitting region. Assuming that rapid minute time scale fluctuations
of the emission is optically thick in radio wavelength, light travel arguments
requires relativistic particle energy, thus suggesting the presence of outflow
from SgrA*.
