  The ultracompact low-mass X-ray binary 4U 0513-40 in the globular cluster
NGC1851 exhibits large amplitude X-ray flux variations with spectral changes
from low/hard to high/soft states which have not been reported previously in
other ultracompact X-ray binaries. Using BeppoSAX, CHANDRA and XMM Newton
archival data together with recent INTEGRAL observations, we reveal a clear
sinusoidal periodic signal with a period of ~17 minutes when the source is in a
typical high/soft state with a dominant soft thermal component. The periodicity
disappears when the source is in a low/hard state and the thermal soft
component is not required any more to model the data. These properties indicate
the orbital nature of the detected signal and imply an high inclination angle
of the binary system (>80{\deg}).
