A SEARCH FOR MILLISECOND PULSARS AT GALACTIC LATITUDES -50-DEGREES-LESS-THAN-B-LESS-THAN-20-DEGREES

We have detected 12 new pulsars, including four of the short-period '' recycled'' variety, in a survey using the Arecibo radio telescope at 4 30 MHz. The survey covered 680 square degrees at right ascensions 21(h ) through 02(h) declinations +7 degrees through +30 degrees. Most of t he region falls between Galactic latitudes The minimum detectable flux density for long-period pulsars was approximately -20 degrees and -50 degrees. The minimum detectable flux density for long-period pulsars was approximately 0.5 mJy for declinations +14 degrees < delta < +23 d egrees, rising to 0.7 mJy at the declination extremes. For periods P < 100 ms the minimum detectable flux density increased with decreasing period, especially for large dispersion measures; at P = 1.5 ms and DM = 10 cm(-3) pc the detection threshold was about 10 mJy. Only one pre viously known pulsar lay within the search region, and it was detected easily. The newly discovered short-period pulsars include two isolate d objects: PSR J2322+2057 (P = 4.81 ms, DM = 13 cm(-3) pc), and PSR J2 235+1506 (P = 59.8 ms, DM = 18 cm(-3) pc); and two pulsars in nearly c ircular binary orbits: PSR J2229+2643 (P = 2.98 ms, DM = 23 cm(-3) pc, orbital period P-b = 93d), and PSR J2317+1439 (P = 3.45 ms, DM = 22 c m(-3) pc, P-b = 2.(d)5). We present timing observations of three of th ese pulsars over 1.5-2.5 yr. Refined and extended data sets for PSRs J 2235+1506 and J2317+1439 have allowed the first measurements of their proper motions, which imply velocities of (100 +/- 40) km s(-1) and (7 0 +/- 30) km s(-1), respectively. Timing measurements of PSR J2229+264 3 show that it has the smallest period derivative of any known pulsar, P over dot = (1.9 +/- 0.2) x 10(-21). We use this result to establish a new upper limit for the possible rate of change of the Newtonian co nstant of gravity, \G over dot/G\ < 3 x 10(-11) yr(-1).