  (Abridged) We present the first Laser Guide Star Adaptive Optics (LGS-AO)
observations of the Galactic center. LGS-AO has dramatically improved the
quality, robustness, and versatility with which high angular resolution
infrared images of the Galactic center can be obtained with the W. M. Keck II
10-meter telescope. Specifically, Strehl ratios of 0.7 and 0.3 at L'[3.8
micron] and K'[2.1 micron], respectively, are achieved in these LGS-AO images.
During our observations, the infrared counterpart to the central supermassive
black hole, Sgr A*-IR, showed significant infrared intensity variations, with
observed L' magnitudes ranging from 12.6 to 14.5 mag. The faintest end of our
L' detections, 1.3 mJy (dereddened), is the lowest level of emission yet
observed for this source by a factor of 3. No significant variation in the
location of SgrA*-IR is detected as a function of either wavelength or
intensity. Near a peak in its intensity, we obtained the first measurement of
SgrA*-IR's K'-L' color (3.0 +- 0.2 mag, observed), which corresponds to an
intrinsic spectral index of -0.5 +- 0.3. This is significantly bluer than other
recent infrared measurements. Because our measurement was taken at a time when
Sgr A* was ~6 times brighter in the infrared than the other measurements, we
posit that the spectral index of the emission arising from the vicinity of our
Galaxy's central black hole may depend on the strength of the flare, with
stronger flares giving rise to a higher fraction of high energy electrons in
the emitting region.
