ROSAT observations of the binary millisecond pulsar PSR j0751+1807

We report the discovery of the binary millisecond pulsar PSR J0751+1807 in the soft X-ray domain with ROSAT. The low number of source counts does not allow a detailed spectral modelling. Assuming an energy spectrum similar to that of PSR J0437-4715 implies, for the pulsar X-ray flux, f(x) similar to 1 x 10(-13) erg s(-1) cm(-2) within the 0.1-2.4 keV energy range. This corresponds to an X-ray luminosity of L(x) similar to 4.7 x 10(31) erg s(-1) if we adopt the dispersion measure based pulsar distance of 2 kpc. A photon arrival time analysis does not reveal significant X-ray pulses. A sine-wave fit to the folded light curve results in a 2 sigma pulsed fraction upper limit of 35 per cent.