Timing the eccentric binary millisecond pulsar in NGC 1851

Abstract

We have used the Green Bank Telescope to observe the millisecond pulsar PSR J0514-4002A on 43 occasions spread over 2 years. This 5 ms pulsar is located in the globular cluster NGC 1851; it belongs to a binary system and has a highly eccentric (e=0.888) orbit. We have obtained a phase-coherent timing solution for this object, including very precise position, spin, and orbital parameters. The pulsar is located 4.6'' (about 1.3 core radii) from the center of the cluster and is likely to lie on its more distant half. The nondetection of eclipses at superior conjunction can be used, given the peculiar geometry of this system, to rule out the possibility of an extended companion. We have measured the rate of advance of periastron for this binary system to be ω= 0.01289(4)° yr^-1, which if due completely to general relativity implies a total system mass of 2.453(14) M. Given the known mass function, the pulsar mass has to be <1.5 M, and the mass of the companion has to be >0.96 M, implying that it is a heavy white dwarf. The 350 MHz flux density of this pulsar varies between 0.2 and 1.4 mJy; the origin of these variations is not known.