  The orbital period of Scorpius X-1 has been accepted as 0.787313 d since its
discovery in archival optical photometric data by Gottlieb, Wright, & Liller
(1975). This period has been confirmed in both photometric and spectroscopic
optical observations, though to date only marginal evidence has been reported
for modulation of the X-ray intensity at that period. We have used data taken
with the RXTE All Sky Monitor to search for such a modulation. A major
difficulty in detecting the orbit in X-ray data is presented by the flaring
behavior of Sco X-1, which contributes white noise to Fourier transforms of the
intensity time series, and tends to obscure weak modulations. We present a new
technique for substantially reducing the effects of the flaring behavior while
retaining much of any periodic orbital modulation, provided only that the two
temporal behaviors exhibit different spectral signatures. Through such a
search, we have found evidence for orbital modulation at about the 1% level
with a period of 0.78893 d, equal within our accuracy to a period which differs
by 1 cycle per year from the accepted value. If we compare our results with the
period of the 1 year sideband cited by Gottlieb et al. we conclude that the
actual period may be 0.78901 d.
