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Joanna M. Rankin (U. Vermont), Avinash A. Deshpande (Raman Research Institute, Bangalore, India)
A nearly coherent sequence of ``drifting" pulses from PSR B0943+10 has led us to develop a technique for mapping the pattern of polar-cap ``storms" or ``sparks" responsible for its emission. We have developed procedures which compute both this ``cartographic" transform and its inverse, in order first to study the character of the polar-cap emission ``map" and then to confirm that this ``map" in turn reproduces the observed pulse sequence.
The application of this technique to pulsar 0943+10 and to other pulsars with regular patterns of subpulse emission provides a basis for assessing the physical origins of ``drifting" subpulse emission---which in turn is one of the most carefully articulated aspects of the Ruderman & Sutherland (1975) theory.
We have studied 0943+10 pulse sequences in both the bright ``B" (profile) mode and ``quiescent" ``Q" mode, and our accurate polarimetric observations at both 430 and 111.5 MHz show that the pulse train is comprised of different polarization-modal contributions. On this basis, we have computed polar-cap emission ``maps" corresponding to these different observations and modal sequences. We find that, strangely, most of the emission comes from the part of the polar cap prior to the magnetic axis, and this circumstance raises the possibility of propagation effects (absorption and/or refraction) within the pulsar magnetosphere which may be responsible for the ``absorption" phenomenon. We further find that pulsar 0943+10 is an ``antipulsar", contrary to the expectations of Ruderman & Sutherland, but has an inside (poleward) sight-line traverse as favored by Arons & Scharlemann (1979).
A number of other pulsars are known with highly regular patterns of subpulse modulation, and this number is likely to increase as the interrupting effect of pulse nulling is better understood. Pulsars with central sight-line traverses, such as B1237+25 or B1919+21, also provide illuminating objects of study.
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