  The discovery of quasi-periodic brightness oscillations (QPOs) in the X-ray
emission accompanying the giant flares of the soft gamma-ray repeaters SGR
1806-20 and SGR 1900+14 has led to intense speculation about their nature and
what they might reveal about the interiors of neutron stars. Here we take a
fresh look at the giant flare data for SGR 1806-20, and in particular we
analyze short segments of the post-peak emission using a Bayesian procedure
that has not previously been applied to these data. We find at best weak
evidence that any QPO persists for more than $\sim 1$ second; instead, almost
all the data are consistent with a picture in which there are numerous
independently-excited modes that decay within a few tenths of a second. This
has interesting implications for the rapidity of decay of the QPO modes, which
could occur by the previously-suggested mechanism of coupling to the MHD
continuum. The strongest QPOs favor certain rotational phases, which might
suggest special regions of the crust or of the magnetosphere. We also find
several previously unreported QPOs in these data, which may help in tracking
down their origin.

High Energy Astrophysical Phenomena