Core and conal component analysis of pulsar B1237+25 - II. Investigation of the segregated modes

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 230 km - 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.