2 NEWLY DISCOVERED MILLISECOND PULSARS

Two millisecond pulsars have been discovered in the course of systematic surveys being made with the Arecibo radio telescope. PSR J2019 + 2425 has a 3.935 ms period and moves in a nearly circular, 76.5 day orbit around a approximately 0.3 M. companion. PSR J2322 + 2057, with a period of 4.808 ms, is an isolated object. The two pulsars have unusually small period derivatives, corresponding to spin-down time scales of 7.5 +/- 0.5 and 11 +/- 5 Gyr, respectively. Both objects show pulse time-of-arrival residuals no larger than a few microseconds over many months, lending further support to the observation that ''recycled'' pulsars have extremely stable rotational behavior. The timing results also confirm that physics related to the rotational dynamics of these strongly self-gravitating stars-in particular, the value of the gravitational coupling constant G-remains essentially constant over time scales comparable to the Hubble time. Dispersion measures of the two pulsars indicate distances of 0.8-0.9 kpc.