Discovery of a Young Radio Pulsar in a Relativistic Binary Orbit

We report on the discovery of PSR J1141-6545, a radio pulsar in an eccentric, relativistic 5 hr binary orbit. The pulsar shows no evidence of being recycled, having a pulse period P = 394 ms, a characteristic age τ c = 1.4 × 10 6 yr, and an inferred surface magnetic dipole field strength B = 1.3 × 10 12 G. From the mass function and measured rate of periastron advance, we determine the total mass in the system to be 2.300 ± 0.012 M ☉ , assuming that the periastron advance is purely relativistic. Under the same assumption we constrain the pulsar's mass to be M p ≤ 1.348 M ☉ , and the companion's mass to be M c > 0.968 M ☉ (both with 99% confidence). Given the total system mass and the distribution of measured neutron star masses, the companion is probably a massive white dwarf that formed prior to the birth of the pulsar. Optical observations can test this hypothesis.