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Z. Srostlik, J. M. Rankin (Univ. of Vermont)
Pulsar B1237+25 is a prime example of a pulsar exhibiting two conal beams and a central core beam. We have carefully studied multiple Arecibo polarimetric pulse sequences of the object that delineate the core component's role in its several modes of behavior. In addition to the pulsar's well-known "normal" and "abnormal" modes, we have identified a third mode which is closely connected with intervals of core-component activity. Third mode "bursts" occur quasi-periodically within normal mode sequences and can be distinguished from normal mode by their distinct average profiles, polarization, and fluctuation phenomena. The third mode is closely associated with a strong clockwise rotation of the polarization angle following the core component and a disruption of the usual 2.8-period normal-mode pulse modulation. 10-20-pulse third-mode "bursts" typically interrupt long normal-mode sequences in this pulsar about every 80 pulses and appear to be responsible for the "core-associated" fluctuation feature, long noted in historical literature as part of normal mode. We emphasize that there are different characters to core activity in the abnormal and third modes, compared with the normal mode where core activity is minimal to undetectable. Our analyses result in improved estimates of the star's emission geometry and the modal polarization variations associated with the three modes.
One of us (ZS) would like to acknowledge Univ. of Vermont HELiX and APLE grants. Portions of this work were carried out with support from NSF Grant AST 99-87654. Arecibo Observatory is operated by Cornell University under contract to the US NSF.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.