Pulsar applications of baseband recording

In this thesis I report on the development and implementation of baseband recording techniques for searches for radio emission from neutron stars. Ultra-bright pulses are a sporadic type of neutron star emission that have intrinsic widths of less than a microsecond. Propagation through the interstellar medium broadens these radio pulses and consequently reduces their peak flux densities. Pre-detection dedispersion can be performed on data taken with baseband recorders to completely mitigate the dispersive aspect of this broadening. However, such ``coherent'' dedispersion is computationally expensive, and so its application has historically been limited to narrow bands and/or short observation times. This thesis describes the first wide-bandwidth searches of large data sets for ultra-bright pulses using pre-detection dedispersion techniques. The equations that determine the efficiency and sensitivity of such searches are presented, and practical data processing algorithms are discussed. The results of large-scale searches for ultra-bright pulses using the Parkes and Green Bank radio telescopes are also presented. These revealed three new emitters -- PSRs J1823-3021A, J0218+4232, and B1957+20. This increases the number of millisecond pulsars documented to emit ultra-bright pulses from two to five. In addition, millisecond pulsars that emit ultra-bright pulses are confirmed to be rare. The ultra-bright pulses from all of the five millisecond pulsar emitters are analysed in further detail. Three of these pulsars emit pulsed X-rays. The phases of the ultra-bright pulses always correlate in phase with the X-ray pulses, but have variable phase relations to ordinary radio emission. Structure in the emission of PSRs B1937+21 and J1824-2452A is seen at timescales as short as 8 and 20ns, respectively. The ultra-bright pulses of PSR J1824-2452A are found to be highly elliptically polarised. Their position angles vary widely. This may mean that local effects are dominating over the global magnetic field during the emission events. However, I also report the likely detection of an ultra-bright pulse from PSR J1823-3021A that consists of two disjoint bursts. As these must originate from widely separated regions of the pulsar magnetosphere, macroscopic excitations seem to occur during ultra-bright emission events. I also describe searches for ultra-bright pulses and periodic emission from neutron stars in globular clusters. The ultra-bright pulse searches, whilst not revealing any new emitters, place new bounds on the existence of energetic millisecond pulsars. The Fourier-domain searches of globular clusters revealed 42 previously known pulsars. One new pulsar is reported -- PSR J0024-7204Z in 47 Tucanae.