Drifting subpulse survey at 21 cm

We present the statistical results of a systematic, unbiased search for subpulse modulation of 187 pulsars performed with the Westerbork Synthesis Radio Telescope (WSRT) in the Netherlands at an observing wavelength of 21 cm (Weltevrede et al. 2006a). We have increased the list of pulsars that show the drifting subpulse phenomenon by 42, indicating that more than 55% of the pulsars that show this phenomenon. The large number of new drifters we have found allows us, for the first time, to do meaningful statistics on the drifting phenomenon. We find that the drifting phenomenon is correlated with the pulsar age such that drifting is more likely to occur in older pulsars. Pulsars that drift more coherently seem to be older and have a lower modulation index. Contrary claims from older studies, both P_3 (the repetition period of the drifting subpulse pattern) and the drift direction are found to be uncorrelated with other pulsar parameters.