Discovery of a pulsar in a binary system.

We have detected a pulsar with a pulsation period that varies systematically between 0.058967 and 0.059045 sec over a cycle of 0.3230 d. Approximately 200 independent observations over 5-minute intervals have yielded a well-sampled velocity curve which implies a binary orbit with projected semimajor axis sin i = 1.0 solar radius, eccentricity e = 0.615, and mass function f(m) = 0.13 solar mass. No eclipses are observed. We infer that the unseen companion is a compact object with mass comparable to that of the pulsar. In addition to the obvious potential for determining the masses of the pulsar and its companion, this discovery makes feasible a number of studies involving the physics of compact objects, the astrophysics of close binary systems, and special- and general-relativistic effects.