A schematic pulsar search is shown in Fig. 11 . The finite bandwidth is split up into a number of channels, typically using a filterbank or a correlator (see e.g. ), either of which usually provides a much finer frequency channelisation than the eight channels shown for illustrative purposes in Fig. 11 . The channels are then de-dispersed (see § 3.1.2) to form a single noisy time series. An efficient way to find a periodic signal in these data is to take the Fast Fourier Transform (FFT) and plot the resulting amplitude spectrum. For a narrow pulse the spectrum will show a family of harmonics. To detect weaker signals still, a harmonic summing technique is usually implemented . The best candidates are saved and the whole process is repeated for another trial DM.
After the data have been processed for a suitable range of DM, a list of pulsar candidates is compiled and the raw time series data are folded modulo each candidate period. In practise the analysis is often hampered by the presence of periodic interference sources which can often look very ``pulsar-like''. Although interference excision schemes (usually based on coincidence analyses of data taken from different points on the sky) work fairly well, interference is an ever-increasing problem in radio astronomy and considerable efforts are required to carry out sensitive searches.
|Binary and Millisecond Pulsars at the New Millennium
Duncan R. Lorimer
© Max-Planck-Gesellschaft. ISSN 1433-8351
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