PSR J1756-2251: A new relativistic double neutron star system

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.degrees585 +/- 0.degrees002 yr(-1). Assuming this is entirely due to general relativity implies a total system mass ( pulsar plus companion) of 2.574 +/- 0.003 M-circle dot. This mass and the significant orbital eccentricity suggest that this is a double neutron star system. Measurement of the gravitational redshift, gamma, and an evaluation of the Shapiro delay shape, s, indicate a low companion mass of less than. The expected coalescence time due to emission of gravitational 1.25 M-circle dot. waves is only similar to1.7 Gyr, substantially less than a Hubble time. We note an apparent correlation between spin period and eccentricity for normally evolving double neutron star systems.