Parkes observations for project P1030 semester 2019OCTS_02

The popular carousel model used to explain subpulse drifting in pulsars is criticised on both physical and empirical grounds. In the absence of relativistic effects (aberration and retardation, AR), it predicts that subpulses undergo only amplitude modulation (i.e. no phase modulation) as a function of frequency. A recently advanced model incorporates AR effects and predicts a subpulse phase shift whose magnitude depends crucially on the assumption of the carousel model that the subpulses originate in discrete structures (sparks) that exist very close to the pulsar's surface. We propose to test this theory by measuring the subpulse phase shift of three pulsars which all exhibit different kinds of frequency evolution of their profiles. This requires both high time resolution of single-pulse data and a wide frequency band, as uniquely offered by the UWL. Our primary target (B1857-26) satisfies all of the conditions required by the proposed test. Two other targets (B1944+17 and B2003-08) also offer unique opportunities to study frequency-dependent subpulse phase shifting in the presence of rare phenomena relating to profile evolution and subpulse drifting. We anticipate that the study of these three pulsars will enable us to conclusively determine whether the carousel model and AR effects are able to account for the frequency-dependent behaviour of individual subpulses.