Core and conal component analysis of pulsar B1237+25

Abstract

This paper provides a new analysis of this famous five-component (M) pulsar. In addition to the core-active 'abnormal' mode of the star, we find two distinct behaviours within its 'normal' mode, a 'quiet-normal' mode with regular 2.8-period subpulse modulation and little or no core activity, and a 'flare-normal' mode, where the core is regularly bright and a nearly four-period modulation is maintained. The flare-normal mode appears to be an intermediate state between the quiet-normal and abnormal behaviours. Short 5-15-pulse flare-normal-mode 'bursts' and quiet-normal intervals alternate with each other quasi-periodically, making a cycle some 60-80 pulses in duration. Abnormal-mode intervals are interspersed within this overall cycle, usually persisting for only a few pulses, but occasionally lasting for scores or even many hundreds of pulses. Within subsequences where the core is exceptionally quiet, the pulsar provides a nearly 'text-book' example of a central sightline traverse - with a polarization-angle sweep rate measured to be at least some 180° deg -1. On this basis it is shown that the sightline impact angle β must be ∼0°.25 or some 5 per cent of the outer conal beam radius. The core component of the star is found to be incomplete, despite the fact that the full antisymmetric circularly polarized signature of the core is present. The visible core component aligns with the trailing right-hand (RH) portion of the circular signature. Measures either of the circular signature or of the trailing half of the core, however, reiterate the roughly 2.6° angular diameter of the polar cap of the star. We find that the PA traverse of the star is disrupted through the action of orthogonally polarized linear power in the longitude range of the core component. This circumstance can be seen in the 'hook' under the core component which usually entails four sense reversals of the PA, with its centre falling at the same PA as the extrema of the overall traverse. This behaviour is modelled to show its effect. Finally, the star provides two well-defined fiducial points from which emission-height estimates can be computed, the respective centres of both the linear PA traverse and the zero-crossing point of the circular polarization signature. We thus find that the outer and inner cones are emitted at heights of some 340 ± 79 and 278 ± 76 km, respectively, such that their field-line 'feet' are some 78 ± 7 and 53 ± 5 per cent of the polar cap radius. We also find evidence that the core emission occurs at a height of some 60 km. © 2005 RAS.