Evidence for an X-ray period in the `Sco-like' source 2S0614+091

A class of galactic X-ray source exists whose members show properties which have many similarities to those of Sco X-1, the brightest source in the X-ray sky^1-3. The X-ray emission from such sources is widely believed to arise from the transfer of matter on to a compact object in a close binary system, but despite extensive observations in many regions of the electromagnetic spectrum there has been little direct evidence to support this view. A study of the temporal behaviour of these Sco-like sources, using data from the Ariel V Sky Survey Instrument (SSI) is in progress; we report here the results of a detailed analysis for one such source, 2S0614+091, which undergoes significant variations in its X-ray intensity consistent with a period of 5.2+/-0.3 days. This is the first discovery of a periodic modulation in the X-ray emission from this class of source and, despite problems regarding the mass-transfer mechanism, provides evidence for their binary nature. Our result has wider implications if 2S0614+091 is confirmed to be an X-ray burster.