The main-interpulse interaction of PSR B1702-19

Aims. This paper reports on single-pulse radio observations of PSR B1702-19 and their implications for pulsar emission theories. Methods. These observations were made with the Westerbork Synthesis Radio Telescope at 1380 and 328 MHz. The PA-swing is used to constrain possible geometries of the pulsar and the single-pulse data is analysed for subpulse modulation correlations between the main pulse and interpulse. Results. We confirm earlier conclusions that the dipole axis of this pulsar is almost perpendicular to its rotation axis, and report that both its main pulse and interpulse are modulated with a periodicity around 10.4 times the pulsar's rotation. Allowing for the half-period delay between main pulse and interpulse the modulation is found to be precisely in phase. Despite small secular variations in the periodicity, the phase-locking continues over all timescales ranging up to several years. Conclusions. The precision of the phase locking is difficult for current emission theories to explain if the main pulse and interpulse originate from opposing magnetic poles. We therefore also explore the possibility of a bidirectional model, in which all the modulated emission comes from one pole, but is seen from two sides and slightly displaced by aberration and time-delay. In this model the unmodulated emission is directed to us from the opposite pole, requiring the emission of the main pulse to originate from two different poles. This is difficult to reconcile with the observed smooth PA-swing. Whichever model turns out to be correct, the answer will have important implications for emission theories.