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 for being recycled , having pulse period P = 394 ms , characteristic age \tau _ { c } = 1.4 \times 10 ^ { 6 } yr , and inferred surface magnetic dipole field strength B = 1.3 \times 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 \pm 0.012 ) M _ { \odot } , assuming that the periastron advance is purely relativistic .
Under the same assumption , we constrain the pulsar ’ s mass to be M _ { p } \leq 1.348 M _ { \odot } and the companion ’ s mass to be M _ { c } \geq 0.968 M _ { \odot } ( both 99 % confidence ) .
Given the total system mass and the distribution of measured neutron star masses , the companion is probably a massive white dwarf which formed prior to the birth of the pulsar .
Optical observations can test this hypothesis .