Glitches in southern pulsars

Timing observations of 40 mostly young pulsars using the ATNF Parkes radio telescope between 1990 January and 1998 December are reported. In total, 20 previously unreported glitches and 10 other glitches were detected in 11 p ulsars, These included 12 glitches in PSR J1341-6220, corresponding to a gl itch rate of 1.5 glitches per year. We also detected the largest known glit ch, in PSR J1614-5047, with Delta nu(g)/nu approximate to 6.5 X 10(-6), whe re nu = 1/P is the pulse frequency. Glitch parameters were determined both by extrapolating timing solutions to interglitch intervals and by phase-coh erent timing fits across the glitch(es), These fits also give improved posi tions and dispersion measures for many of the pulsars, Analysis of glitch p arameters, both from this work and from previously published results, shows that most glitches have a fractional amplitude Delta nu(g)/nu of between 1 0(-8) and 10(-6). There is no consistent relationship between glitch amplit ude and the time since the previous glitch or the time to the following gli tch, either for the ensemble or for individual pulsars. As previously recog nized, the largest glitch activity is seen in pulsars with ages of order 10 (4) yr, but for about 30 per cent of such pulsars, no glitches were detecte d in the 8-year data span. There is some evidence for a new type of timing irregularity in which there is a significant increase in pulse frequency ov er a few days, accompanied by a decrease in the magnitude of the slowdown r ate. Fits of an exponential recovery to post-glitch data show that for most older pulsars, only a small fraction of the glitch decays. In some younger pulsars a large fraction of the glitch decays, but in others there is very little decay. Apart from the Crab pulsar, there is no clear dependence of recovery time-scale on pulsar age.