On the X-ray fast-time variability of Sco X-2 (GX 349+2)

We have analysed archived Ginga data on the Z source Sco X-2 (GX 349+2). We present the first detailed investigation of its X-ray fast-time variabilit y, as a function of position in the Z track. During the two-day observation over the period 5-7 March 1989, the source was in the so-called flaring br anch, and the lower part of the so-called normal branch. We:e found broad p eaked noise with a centroid frequency and width of similar to4-7 Hz and sim ilar to6-12 Hz respectively. The peaked noise was strongest in the lower fl aring branch, with a maximum fractional rms amplitude of similar to3%. We c onclude that it is not a manifestation of atoll source high frequency noise , as had been suggested, and compare it with the power spectral features se en in other Z sources. We find that the peaked noise is markedly different to the quasi-periodic oscillations found in the normal and flaring branches of Sco;X-1, however it bears some resemblance to that seen in the flaring branch of Cyg X-2 at low overall intensities.