Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt.........3j&link_type=abstract
Thesis (PhD). STANFORD UNIVERSITY, Source DAI-B 60/04, p. 1650, Oct 1999, 193 pages.
Astronomy and Astrophysics
Astronomy
Scientific paper
High-energy γ-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 μs. The opportunity to analyze high-quality γ-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 γ-ray bursts independent of triggers from other γ-ray instruments is developed. Several known γ-ray bursts were independently detected, and there is evidence for a previously unknown γ-ray burst candidate. Statistical methods using maximum likelihood and Bayesian inference are developed and implemented to extract periodic signals from γ-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 γ-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 γ-ray beam at SLAC. The reconstruction software was used to determine the incident γ-ray direction. It was found that the simulations did an excellent job of representing the actual instrument response.
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