2005ApJ...618L.119F

We report the discovery during the Parkes Multibeam Pulsar Survey of PSR J1756-2251, a 28.5 ms pulsar in a relativistic binary system. Subsequent timing observations showed the pulsar to have an orbital period of 7.67 hr and an eccentricity of 0.18. They also revealed a significant advance of periastron, 2°.585±0°.002/yr. Assuming this is entirely due to general relativity implies a total system mass (pulsar plus companion) of 2.574±0.003 M_☉. This mass and the significant orbital eccentricity suggest that this is a double neutron star system. Measurement of the gravitational redshift, γ, and an evaluation of the Shapiro delay shape, s, indicate a low companion mass of less than 1.25 M_☉. The expected coalescence time due to emission of gravitational waves is only ∼1.7 Gyr, substantially less than a Hubble time. We note an apparent correlation between spin period and eccentricity for normally evolving double neutron star systems.