Type of Document Dissertation Author Collazzi, Andrew URN etd-06282011-141122 Title Testing and Improving the Luminosity Relations for Gamma-Ray Bursts Degree Doctor of Philosophy (Ph.D.) Department Physics & Astronomy Advisory Committee
Advisor Name Title Schaefer, Bradley E. Committee Chair Browne, Dana Committee Member Frank, Juhan Committee Member Hynes, Robert Committee Member Deng, Zhi-Qiang Dean's Representative Keywords
Date of Defense 2011-06-16 Availability unrestricted AbstractGamma Ray Bursts (GRBs) have several luminosity relations where a measurable property of a burst light curve or spectrum is correlated with the burst luminosity. These luminosity relations are calibrated for the fraction of bursts with spectroscopic redshifts and hence the known luminosities. GRBs have thus become known as a type of "standard candle"; where standard candle is meant in the usual sense that their luminosities can be derived from measurable properties of the bursts. GRBs can therefore be used for the same cosmology applications as Type Ia supernovae, including the construction of the Hubble Diagram and measuring massive star formation rate. The greatest disadvantage of using GRBs as standard candles is that their accuracy is lower than desired. With the recent advent of GRBs as a new standard candle, every effort must be made to test and improve the distance measures.
Here, several methods are employed to do just that. First, generalized forms of two tests are performed on all of the luminosity relations. All the luminosity relations pass the second of these tests, and all but two pass the first. Even with this failure, the redundancy in using multiple luminosity relations allows all the luminosity relations to retain value. Next, the "Firmani relation" is shown to have poorer accuracy than first advertised. In addition, it is shown to be exactly derivable from two other luminosity relations. For these reasons, the Firmani relation is useless for cosmology. The Amati relation is then revisited and shown to be an artifact of a combination of selection effects. Therefore, the Amati relation is also not good for cosmology. Fourthly, the systematic errors involved in measuring a popular luminosity indicator (Epeak) are measured. The result is that an irreducible systematic error of 28% exists. After that, a preliminary investigation into the usefulness of breaking GRBs into individual pulses is conducted. The results of an "ideal" set of data do not provide for confident results due to large error bars. Finally, the work concludes with a discussion about the impact of the work and the future of GRB luminosity relations.
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