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Timing Observations of the J1518+4904 Double Neutron Star System

We summarize timing observations of PSR J1518+4904, a recently discovered pulsar in a double neutron star binary. New measurements include (1) periastron advance of 0:0113 0:0001 yr ?1 , for a total system mass of 2:69 0:04 M ; (2) period derivative of 2 10 ?20 , yielding an age comparable to that of the Galaxy and a magnetic eld substantially lower than other pulsars in double neutron star binaries; and (3) proper motion of 8 2 mas yr ?1 , or a transverse velocity of 27 8 km s ?1 , among the lowest pulsar velocities measured. Observations PSR J1518+4904 is a 40.9 ms pulsar in a moderately eccentric, 8.6 day orbit with a second neutron star. It was discovered in the course of a recent survey of the northern sky for fast pulsars (Sayer, Nice & Taylor 1997). We have made timing observations of this pulsar with the Green Bank 140 Foot Telescope at regular intervals since its discovery. The dataset extends from December 1994 to November 1996, and includes observations made at 370, 575, and 800 MHz. Further details of the data acquisition system, as well as results from an early portion of the data, are given in Nice, Sayer, & Taylor (1996).