We present new results of timing and single-pulse measurements for 18 radio pulsars discovered in 1993-1997 by the Penn State / Naval Research Laboratory declination-strip survey conducted with the 305 m Arecibo Telescope at 430 MHz. Long-term timing measurements have led to significant improvements of the rotational and the astrometric parameters of these sources, including the millisecond pulsar, PSR J1709+2313, and the pulsar located within the supernova remnant S147, PSR J0538+2817. Single-pulse studies of the brightest objects in the sample have revealed an unusual ''bursting'' pulsar, PSR J1752+2359, two new drifting subpulse pulsars, PSR J1649+2533 and PSR J2155+2813, and another example of a pulsar with profile mode changes, PSR J1746+2540. PSR J1752+2359 is characterized by bursts of emission, which appear once every 3-5 minutes and decay exponentially on a $45 s timescale. PSR J1649+2533 spends $30% of the time in a null state with no detectable radio emission.

Accurate, long-term timing measurements of pulsars provide a powerful method to study a variety of astrophysical phenomena. For "normal", slow pulsars, the dominant factors that limit the timing precision are the intrinsic timing noise and single pulse "jitter" (e.g. Cordes 1993). In fact, because the pulse jitter surpasses radiometer noise for sufficiently strong pulsars and no further improvement of the timing precision can be achieved by increasing the antenna gain, the timing of such sources can be very efficiently conducted with suitably equipped medium-size radiotelescopes.We have been timing slow pulsars with the 32-m TCfA radiotelescope in Toruri, Poland, since July 1996, using a dual-channel, circular polarization Lband receiving system at frequencies around 1.7 GHz, and a 2 X 64 X 3 MHz channel pulsar backend, the Penn State Pulsar Machine -2 (PSPM-2; for more details, see Konacki et al. 1999). Our gradually expanding source list currently includes 88 pulsars timed once a week with a millisecond precision using the observatory's UTC-calibrated H-maser clock. Data analysis is routinely performed with the T E M P O 1 software package. With a particularly dense, weekly sampling and a < 1 ms timing precision, the TCfA program has a sensitivity to detect previously overlooked short period, low orbital inclination binaries, as well as very low-mass, planetary companions. In addition, it will be very useful in identifying and monitoring pulsar timing glitches and other forms of the timing noise.Two years of timing of 38 pulsars from our observing list have already produced interesting limits on possible terrestrial-mass companions to some of these objects. The planetary limits, expressed in terms of the orbital period and the planet mass for circular, edge-on orbits, are shown in Fig. l a . Limiting masses were calculated using the rms residuals left over from the best fits of timing models to data. The models included the pulsar period, the spindownThe most recent version is available at http://pulsar.princeton.edu/tempo, which is maintained and distributed by Princeton University and the Australia Telescope National Facility.