PSR J1740-3052 - a pulsar with a massive companion

We report on the discovery of a binary pulsar, PSR J1740-3052, during the Parkes 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 kyr, and is in a 231-day, highly eccentric orbit with a companion whose mass exceeds 11 M_sun. An accurate position for the pulsar was obtained using the Australia Telescope Compact Array. Near-infrared 2.2-um observations make with the telescopes at the Siding Spring observatory reveal a late-type star coincident with the pulsar position. However, we do not believe that this star is the pulsar's companion, because a typical star of this spectral type and required mass would extend beyond the pulsar's orbit. Furthermore, the measured advance of periastron of the pulsar suggests a more compact companion, for example, a main-sequence star with radius only a few times that of the sun. Such a companion is also more consistent with the small dispersion measure variations seen near periastron. Although we cannot conclusively rule out a black-hole companion, we believe the companion is probably an early B star, making the system similar to the binary PSR J0045-7319.