Scorpius X-1

J. Middleditch and W. Priedhorsky, Los Alamos National Laboratory, communicate: "In a search for coherent x-ray pulsations from Sco X-1 we find quasiperiodic fast variability. Fourier analysis of 34 ks of EXOSAT ME data starting on Feb. 26.151 UT shows excess power between 4 and 9 Hz, corresponding to a 3-percent rms flux variation. The power spectrum peak has a fwhm of 1 Hz, a centroid near 6 Hz and a statistical significance of 100-sigma. This variability was present only in the last half of the data, when the source was quiescent; it was absent earlier when the source was flaring (to a limit below 1 percent rms of the quiescent flux). This feature may be similar to that reported by van der Klis et al. in GX 5-1 (IAUC 4043) and/or to the 0.6-Hz 'noisar' feature in AM-Her binaries (Middleditch 1982, Ap.J. 257, L71)."