OBSERVATION OF NULLING IN RADIO PULSARS WITH THE OOTY-RADIO-TELESCOPE

The recently upgraded Ooty Radio Telescope was used to observe pulse n ulling in 10 pulsars. The fraction of time a that a pulsar spends in t he nulled state is less than or equal to 2.5 per cent for PSR 0149-16, less than or equal to 7.0 per cent for PSR 0942-13 and 44.6 +/- 1.3 p er cent for PSR 0031 - 07. The remaining seven a-values are consistent with previous estimates. This paper suggests an improved scheme of ob taining a for weak pulsars. In most pulsars, the width of the individu al,pulse is much smaller than that of the integrated pulse. The energy in a pulse can be best estimated by integrating the power over the wi dth of the individual pulse, and not over that of the integrated pulse . An equivalent scheme involves summing up, from each individual pulse , a pre-determined number of extreme-valued powers. This significantly improves the accuracy of the nulling data. This method is used to obt ain the statistics of the burst and null durations in PSR 0031 - 07. B oth phenomena consist of at least two distinct random processes: (a) a short-time-scale process that can be represented by an exponential di stribution with a width of approximate to 2.5 periods, and (b) a long- time-scale process that can be represented, for the burst phenomenon, by a Rayleigh distribution with a width of approximate to 24 periods. The duration of a burst is weakly correlated with that of the precedin g null. The onset of a burst or a null is usually abrupt, but sometime s occurs over several periods. There is no significant difference betw een the average first and last pulses of a burst.