A search for gamma-ray bursts and pulsars, and the application of Kalman filters to gamma-ray reconstruction.

摘要

High-energy gamma-ray astronomy was revolutionized in 1991 with the launch of the Energetic Gamma-Ray Experiment Telescope (EGRET) on board the Compton Gamma-Ray Observatory. In addition to unprecedented instrument effective area and a narrow point-spread function, EGRET provided photon time-tagging to an absolute accuracy of 100 mus. The opportunity to analyze high-quality gamma-ray data requires sophisticated statistical and analytic tools. Part I describes the analysis of periodic and transient signals in EGRET data. A method to search for the transient flux from gamma-ray bursts independent of triggers from other gamma-ray instruments is developed. Several known gamma-ray bursts were independently detected, and there is evidence for a previously unknown gamma-ray burst candidate. Statistical methods using maximum likelihood and Bayesian inference are developed and implemented to extract periodic signals from gamma-ray sources in the presence of significant astrophysical background radiation. The methods allow searches for periodic modulation without a priori knowledge of the period or period derivative. The analysis was performed on six pulsars and three pulsar candidates. The three brightest pulsars, Crab, Vela, and Geminga, were readily identified, and would have been detected independently in the EGRET data without knowledge of the pulse period. No significant pulsation was detected in the three pulsar candidates. In addition, methods for calculating the detection threshold of periodic flux modulation were developed.;The future hopes of gamma-ray astronomy lie in the development of the Gamma-ray Large Area Space Telescope, or GLAST. Part II describes the development and results of the particle track reconstruction software for a GLAST science prototype instrument beamtest. The Kalman filtering method of track reconstruction is introduced and implemented. Monte Carlo simulations, very similar to those used for the full GLAST instrument, were performed to predict the instrumental response of the prototype. The prototype was tested in a gamma-ray beam at SLAC. The reconstruction software was used to determine the incident gamma-ray direction. It was found that the simulations did an excellent job of representing the actual instrument response.