2000ApJ...543..321K

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=1.4x10⁶ yr, and an inferred surface magnetic dipole field strength B=1.3x10¹² 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.