PSR J1740-3052: a pulsar with a massive companion

We report on the discovery of a binary pulsar, PSR J1740-3052, during the P arkes multibeam survey. Timing observations of the 570-ms pulsar at Jodrell Bank and Parkes show that it is young, with a characteristic age of 350 ky r, and is in a 23 1-d, highly eccentric orbit with a companion whose mass e xceeds 11 M.. An accurate position for the pulsar was obtained using the Au stralia Telescope Compact Array. Near-infrared 2.2-mum observations made wi th the telescopes at the Siding Spring observatory reveal a late-type star coincident with the pulsar position. However, we do not believe that this s tar is the companion of the pulsar, because a typical star of this spectral type and required mass would extend beyond the orbit of the pulsar. Furthe rmore, the measured advance of periastron of the pulsar suggests a more com pact companion, for example, a main-sequence star with radius only a few ti mes that of the Sun. Such a companion is also more consistent with the smal l dispersion measure variations seen near periastron. Although we cannot co nclusively rule out a black hole companion, we believe that the companion i s probably an early B star, making the system similar to the binary PSR J00 45-7319.