On the absence of pulses from pulsars

The aim of this thesis is to investigate the absence of pulses in pulsar, a phenomena also know as pulsar nulling. The motivation for the work done in thesis is listed in Chapter 2. A detailed discussion on the previous work carried out to investigate pulsar nulling phenomena is also included in Chapter 2. Chapter 3 discusses in details all the observations carried out for the thesis. In Chapter 4, details regarding the nulling behaviour of various pulsars are listed. Chapter 4 highlights the fact that nulling is unpredictable. Chapter 5 presents a comparison between two pulsars with high NFs. It is shown that both the pulsars exhibit similar bursting behaviour, but strikingly different quasi-periodicities and emission properties. Chapter 6 discusses the details regarding the simultaneous observations of two nulling pulsars at four different frequencies. These observations suggest that nulling is a frequency independent phenomena simultaneous occuring over a decade of frequency. Chapter 7 summaries the results obtained in three different studies along with their implications. The future work to extend the work carried out in the thesis is also listed in Chapter 7. The main conclusions of the thesis are as follow, (1) NF is not an ideal parameter to quantify nulling behaviour, confirmed firmly by comparing low NF pulsars as well as high NF pulsars, (2) Nulling occurs randomly with unpredictable length durations. Quasi-periodicities seen in the high NF pulsars can also be explained by the Markov models with a forcing function, (3) Nulling is an extreme form of mode-changing phenomena which occurs on a global magnetospheric scale, (4) Geometric reasons are less favoured as a likely cause of nulling phenomena due to the randomness and broadband behaviour reported in this thesis.