Pulsar Nulling Phenomena

DURING an investigation of the short-term behaviour of the radiation coming from pulsars during strong bursts, several objects were found to exhibit pulse nulling phenomena. This was first noted on analogue records of the pulsar radiation intensity where the pen deflexions are a rough measure of the pulse energy. PSR's 0834 + 06, 1133 + 16, 1237 + 25 and 1929 + 10 were found suddenly to miss from one to ten pulses at various times, termed ``nulls'', during otherwise very strong and steady bursts. A null means that the pulse energy decreased by a factor of ten or more over one or two pulse periods and then increased just as sharply after the null. The nulls can be divided into two types according to their duration and their spacing. Type I nulls are the most prominent with a width between three and ten pulses and recur with spacings of about fifty pulses. Type II nulls have a width of only one or two pulses and recur with spacings of three to ten pulses. Pulse sequences from 1133 + 16 and 1237 + 25 and possibly 0834 + 06 contain the Type I nulls while sequences from all four objects contain Type II nulls. A quick look at the spacings of these nulls suggests that they may recur periodically and hence contribute to responses at characteristic periods in pulse energy fluctuation power spectra. This possibility has been reported indirectly by Sutton et al.¹ and Hesse² for the Type II nulls in 0834 + 06 and directly by Lang³ for Type I nulls in 1133 + 16 and 1237 + 25.