  We report on new RXTE X-ray spectral analysis of bursts from SGR 1806-20, the
most prolific SGR source known. Previous studies of bursts from this source
revealed a remarkable lack of spectral variability both in single bursts as
well as from burst to burst. We present here some of the first evidence for
significant spectral evolution within SGR bursts. We find that optically thin
thermal bremsstrahlung (OTTB) spectra including photoelectric absorption
provide the best fits to most bursts, however, other models (power law, Band
GRB) can also produce statistically acceptable fits. We confirm the existence
of a rolloff in the photon number spectrum below 5 keV.
