A Very Luminous Binary Millisecond Pulsar

Abstract

We report the discovery of a field binary millisecondpulsar, J0218+4232, with a period of 2.3 ms and in a 2.0 day binaryorbit with a >~0.16 M�� companion. The new pulsar was serendipitouslydiscovered as a steep-spectrum, highly polarized, compact radio sourceduring imaging observations at Westerbork, and was later confirmedto be a pulsar with observations carried out with the 76 m antennaat Jodrell Bank. With a dispersion measure of 61 pc cm-3, it liesoutside the electron layer in the direction l = 140 deg, b = -18 deg.At a distance of more than 5.7 kpc, it is the farthest known fieldmillisecond pulsar and has a radio luminosity L400 comparable tothat of PSR B1937+21. It appears that a significant fraction of theradio emission is not pulsed. This, together with the extremely broadpulse profile, suggests that we are looking at an aligned rotator.