Kernel density estimators applied to hard X-ray observations of the Crab Pulsar

Carstairs, Ian Ruthven (1992) Kernel density estimators applied to hard X-ray observations of the Crab Pulsar. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The MIFRASO balloon-borne hard X-ray telescope made three observations of the Crab Pulsar during its flights in 1986 and 1987. A number of other objects were also observed, such as the galactic binary systems A0535+ 26, Cygnus X-1 and Hercules X-1, the Seyfert galaxies NGC 4151 and MCG 8-11-11, the quasar 3C273, the Coma galactic cluster and the unusual binary system SS433. The telescope had an energy range of 15-300 keV with a fine timing resolution of 0.33ms. The kernel density estimator (KDE) technique has been recently proposed as an unbiased estimator of pulsar light curves. The KDE technique is an alternative to the traditional binned histogram and has been applied to the MIFRASO observations, providing consistent results which are more sensitive to the shape of the pulsed emission. The accompanying statistical test for phase uniformity, the H_m*PROB*LEM test, has been applied to one of the Crab observations in a periodicity search. The resulting period was found to agree with the radio period of the pulsar, interpolated to a time contemporary with the MIFRASO observations. The traditional tests for phase uniformity, the Pearson and Rayleigh tests, were also investigated and found to be inferior to the new H_m*PROB*LEM test. Spectral deconvolution of the time-averaged Crab Pulsar signal was performed and the resultant power-law fit found to be in good agreement with previous observations. Using the pulse profiles estimated using the KDE technique, the pulsed emission was separated from the unpulsed emission and separately deconvolved. The resultant spectrum is well described by a power-law fit of harder spectral index than the time-averaged spectrum, in agreement with current models of the pulsar emission mechanisms. Finally, a period searching algorithm using the H_m*PROB*LEM test was implemented upon a transputer array, providing significant speedups in execution time. A limited periodicity search of the MIFRASO observation of the X-ray binary Cygnus X-1 using the transputer-implemented H_m*PROB*LEM test failed to reveal any pulsations.