Date of Award


Document Type


Degree Name

Master of Science (MS)




Numerous studies of conal pulsars, e.g. B1133+16, have revealed fluctuation features and a steady null fraction. Sensitive Arecibo observations provide an unprecedented ability to detect nulls and confirm previously found fluctuation features. By replacing each pulse with a scaled version of the average profile, we were able to quench all subpulse modulation, dubbed pulse-modulation quelling (PMQ). It was surprising to note that the low-frequency feature observed in the natural longitude resolved fluctuation spectra (LRF) persisted in the PMQ LRFs! It appears that we can conclude, then, that the nulls themselves reflect whatever underlying periodicity is responsible for the low-frequency feature. Conversely, the aggregate fluctuation power of the low frequency feature changes little whether the pulse modulation is quelled or not, implying that the feature fluctuations are produced by the nulls! These conclusions are perplexing because (with very unusual exceptions) no obvious or regular periodicities have heretofore been attributed to null occurrence.