  We report RXTE/PCA observations of 4U 1608-52 on March 15, 18 and 22
immediately after the outburst in early 1996. The persistent count rates ranged
from 190 to 450 cps (1-60 keV). During this period of time, 4U 1608-52 was in
the island state. We detected QPO features in the power density spectra (PDS)
at 567-800 Hz on March 15 and 22, with source fractional root-mean-square (rms)
amplitude of 13%-17% and widths of 78-180 Hz. The average rms amplitude of
these QPO features is positively correlated with the energy. Our results imply
that the neutron star spin frequency is possibly between 300 Hz and 365 Hz.
