The mode-switching phenomenon in pulsars.

Observations of the mode switching pulsars PSR 0329+54 and PSR 1237+25 during the years 1975-1979 and 1972-1977 with 100 m, 25 m, and 305 m radio telescopes are reported. Observations were sampled at intervals of 0.0003 periods, at least as long as the interstellar dispersion sweep time of the signal across the filter bandwidth. Synchronous mode-switching was found to occur at different frequencies, suggesting broadband emission. Spectra measured at different pulse component peaks were found to be similar in the normal mode, then steepen or flatten in the abnormal mode. All the polarization properties were affected by a mode change, as were the periodic intensity fluctuations from pulse to pulse. The abrupt changes are taken to indicate that the mode-switching phenomena takes place at the pulsar surface, and are due to inhomogeneous chemical composition.