Pulsar PSR 1919+21 - Notches, drifting subpulses, microstructure, and other emission

The radiofrequency dependence of intensity fluctuations of PSR 1919 + 21 is discussed. An intensity model that includes drifting subpulses and an independent zero- and low-frequency (steady) intensity is shown to be quantitatively consistent with the salient features of fluctuation spectra. Drifting subpulses are modeled as Gaussian envelopes that modulate a random intensity, a representation that permits estimation of the separate drifting subpulse and steady contributions to the mean intensity profile. Quantitative evaluation of the model shows that the steady intensity dominates the pulse character above 200 MHz. The results also suggest that microstructure and notches in mean pulse profiles are associated with the drifting subpulses; their absence at 318 MHz may be due to a combination of two effects: (1) the relative weakness of the drifting subpulses at 318 MHz, and (2) the presence of notches, and perhaps microstructure, in the drifting subpulses themselves appears to be frequency dependent. It is suggested that the drifting subpulses and the steady emission originate from different radii in the pulsar magnetosphere. A 0.9-ms upper limit on the interstellar scattering broadening time at 74 MHz is inferred from the observed fractional notch depth. Subject heading: pulsars