The topology and polarization of subbeams associated with the drifting subpulse emission of pulsar B0943+10-VII. Analysis of transitional intervals in the mode-switching process

We report a study of the transitional intervals between pulsar B0943+10's two primary Q and B emission modes using Arecibo 327-MHz observations. The goal of this study was to detect signs of a 'transitional' mode at 327 MHz, discovered recently at lower frequencies. We have found subpulse drift and profile form patterns at 327 MHz similar to those identified at lower frequencies in the Q-to-B mode transition process. Pulse fading during about 15 stellar rotations preceding the appearance of subpulse drift was observed as well. Another part of the work is devoted to a detailed study of the pulse polarization variations in the main modes. A complex behaviour of the linear polarization percentage (LPP) of the dominant first component of the average profile with B-mode age has been found: during the first 4 h, the LPP continuously increases from 5 to 40 per cent, and over the next 1.5 h gradually decreases down to 30 per cent until the subsequent onset of the Q mode. In contrast, the LPP of the second component does not change over the B-mode lifetime, remaining at the level of 22 per cent. A non-instantaneous decrease in the LPP was detected at Q-mode onset. No systematic change of the LPP of the averaged Q-mode pulses over several hours of age was found. The results are discussed within the framework of the core-cone beam model and orthogonal polarization modes.