  We report the first resolved rapid transition from a Flaring Branch
Oscillation to a Normal Branch Oscillation in the RXTE data of the Z source Sco
X-1. The transition took place on a time scale of ~100 seconds and was clearly
associated to the Normal Branch-Flaring Branch vertex in the color-color
diagram. We discuss the results in the context of the possible association of
the Normal Branch Oscillation with other oscillations known both in
Neutron-Star and Black-Hole systems, concentrating on the similarities with the
narrow 4-6 Hz oscillations observed at high flux in Black-Hole Candidates.

Astrophysics