Title page for ETD etd-08302007-084124

Type of Document Dissertation
Author McEwen, Megan Alicia
URN etd-08302007-084124
Title Using Power Spectra To Look For Anisotropies in Ultra-High Energy Cosmic Ray Distributions
Degree Doctor of Philosophy (Ph.D.)
Department Physics & Astronomy
Advisory Committee
Advisor Name Title
James Matthews Committee Chair
Joel Tohline Committee Member
Juhan Frank Committee Member
Kip Matthews Committee Member
Hsiao-Chun Wu Dean's Representative
  • anisotropy
  • astronomy
  • physics
  • high energy physics
  • cosmic rays
Date of Defense 2007-06-29
Availability unrestricted
The origins and compositions of ultra-high energy cosmic rays (UHECR) remains a mystery to this day. The Pierre Auger Observatory (PAO) is being constructed now in the hopes that it will help solve this mystery by detecting more UHECR than any previous experiment. In this dissertation, I will discuss this experiment, and analyze the data collected so far by comparing it with simulated data from possible source distributions. In these simulations, I will track antiprotons, along with other possible cosmic ray primaries, through various models of galactic and extragalactic magnetic fields. Once they reach a certain distance, I will record their positions on the sky. These final positions will determine the weight of that position on the sky. This weight will then be applied to possible source distributions, and the particles will be reinjected back to the earth's surface, and the simulated arrival directions will be analyzed. I will be using the method of calculating spherical harmonics coefficients to analyze the data. The method of using these angular power spectra is an attempt to provide a common language for model builders and experimentalists. Anisotropies of any size are easily detected using these coefficients, making them an ideal way to look at observed events that might not be coming from single, point sources. I will compare the results of this analysis with data obtained by the PAO by calculating spherical harmonics coefficients. After comparing the events collected to date by the PAO with three possible source distributions-isotropic, Active Galactic Nuclei, and nearby galaxies-I have observed that the data looks consistent with either nearby galaxies or AGNs as sources. However, there does exist an extra dipole moment inherent to a half-sky exposure, such as the PAO currently has, which adds in an uncertainty that fundamentally undermines the capabilities of large-scale anisotropy analysis. In the absence of clear point-like sources, construction of a detector in the Northern hemisphere will be necessary in order to know the origins of UHECRs with any confidence.
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