2013MNRAS.435.1984S

Radio pulsar B1237+25 is the prime exemplar of a five-component profile indicating a core/double cone emission-beam structure. Here we conduct a pulse-sequence analysis of its three behaviours based on our earlier partial profile study in Paper I. Focusing on the core region, we find first that its two `orthogonal' polarization modes are far from orthogonal and second that aberration/retardation (A/R) of the secondary orthogonal polarization mode is responsible. As expected this A/R effect is seen both in the retarded core power and the delayed polarization-angle signature. The A/R effect thus seems to reflect a cascade or amplifying process along the magnetic axis extending to a height of some 230km - indeed, very similar to what was found earlier for pulsar B0329+54. The pulsar's three `states' reflect different conditions of core activity: in the quiet-normal mode, core emission is barely perceptible, and the two cones exhibit phase-locked modulation in the manner of a carousel beam system. In the flare-normal mode, this modulation persists for short intervals, while the core is more active, exhibiting intensity-dependent A/R associated mainly with a single, apparently X, propagation mode. Finally, in the abnormal mode, the intensity-dependent A/R-associated core emission is continuous - the primary X trailing and secondary O leading - and appears to distort and retard the conal O-mode emission and quench its modulation.