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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 min 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 (&gt;80°).

The 17‐min orbital period in the ultracompact X‐ray binary 4U 0513‐40