We report analysis of an 8 hr observation of PSR B0943+10 at 325 MHz performed at the Giant Metrewave Radio Telescope (GMRT) in India. B0943+10 is well known for displaying regular sub-pulse drifting and two emission modes. We investigate the modal b
ehavior of B0943+10. By reconstructing an entire B mode from two consecutive B modes, we estimate that the pulsar spends roughly 7.5 hrs in the B mode and about 2.2 hrs in the Q mode, on average. Although the pulsar can switch modes within one pulse, the sub-pulse drift rate changes with a characteristic time of 1.2 hrs over the course of a B mode. Under the subbeam carousel model we find the drift-rate changes are produced by a 10% increase in the average number of subbeams and a 16% increase in the carousel circulation time. We speculate that under the partially screened gap model the increase in circulation time should be related to a small increase in the neutron star surface temperature.
This paper reports new observations of pulsars B0943+10 and B1822--09 carried out with the Arecibo Observatory (AO) and the Giant Metrewave Radio Telescope (GMRT), respectively. Both stars exhibit two stable emission modes. We report the discovery in
B0943+10 of a highly linearly polarized precursor component that occurs primarily in only one mode. This emission feature closely resembles B1822-09s precursor which also occurs brightly in only one mode. B0943+10s other mode is well known for its highly regular drifting subpulses that are apparently produced by a rotating carousel system of 20 beamlets. Similary, B1822-09 exhibits subpulse-modulation behavior only in the mode where its precursor is absent. We survey our 18 hours of B0943+10 observations and find that the sideband-modulation features, from which the carousel-rotation time can be directly determined, occur rarely--less than 5% of the time--but always indicating 20 beamlets. We present an analysis of B1822-09s modal modulation characteristics at 325-MHz and compare them in detail with B0943+10. The pulsar never seems to null, and we find a 43-rotation-period feature in the stars Q mode that modulates the interpulse as well as the conal features in the main pulse. We conclude that B1822-09 must have a nearly orthogonal geometry and that its carousel circulation time is long compared to the modal sub-sequences available in our observations, and the mainpulse/interpulse separation is almost exactly 180 degrees. We conclude the precursors for both stars are incompatible with core-cone emission. We assess the interesting suggestion by Dyks et al. that downward-going radiation produces B1822-09s precursor emission.
