The drift modes of pulsar B0943+10

Pulsar B0943+10 is well known for its 'B' (burst) mode, characterized by accurately drifting subpulses, in contrast to its chaotic 'Q' (quiet) mode. Six new Arecibo observations at 327 MHz, with durations of 2+ hours each, shed considerable light on the modal dynamics of this pulsar. Of these, three were found to be exclusively 'B' mode, and three were discovered to exhibit transitions from the 'Q' to the 'B' mode. One of these observations permitted determination of the subbeam-carousel circulation time in the 'Q' mode for the first time, at some 36.4 +/- 0.9 stellar-rotation periods. The onset of the 'B' mode was observed to commence similarly in all three observations. The initial circulation time of about 36 periods relaxed to nearly 38 periods in a roughly exponential fashion with a characteristic time of an hour-the longest characteristic time known in a mode-switching pulsar. Moreover, at 'B'-mode onset the pulsar exhibits a symmetrical resolved-double profile form with a stronger trailing component; but this component slowly dies away leaving the usual single 'B'-mode profile with the longitude of the magnetic axis failing at about its trailing half power point. None of this, however, elucidates how 'B'- and 'Q'-mode intervals alternate within an overall cycle. We report the first observations of this full modal cycle using the Westerbork telescope.