Doctor of Philosophy

dissertationThe majority of the known extragalactic very high energy (E>100 GeV) gamma ray emitting objects are blazars, active galactic nuclei with relativistic jets aligned close to the line of sight. Due to this geometry, the location of the gamma-ray emission along the jet is unclear. M87 is a nearby radio galaxy with its jet misaligned with the line of sight. The proximity of M87 and the jet misalignment allow detailed studies of spatially resolved emission regions in the radio, optical, and X-ray wavebands. The jet is unresolved in the gamma-ray regime, but contemporaneous flux variability measurements with other wavelengths provide a unique opportunity to constrain the emission origin and mechanisms responsible for high energy gamma-ray emission from an active galactic nucleus. Ground-based imaging telescopes are used to observe the gamma-ray sky by detecting the Cherenkov light from the electromagnetic cascade initiated by gamma rays interacting with the Earth's atmosphere. The Very Energetic Radiation Imaging Telescope Array System (VERITAS) has monitored very high energy gamma-ray emission from M87 since 2007. Over 170 hours of M87 observations have been performed by the VERITAS array between 2007 and 2010. Flaring activities have been observed in 2008 and 2010 with flux variability in the time scale of days and with flux level up to 10 times the average nonflaring flux of M87. The shortest variability time scale observed by VERITAS is 0.9 days, which constrains the size of the emission region. Simultaneous multiwavelength observations from radio to TeV gamma rays during the 2009 nonflaring period yielded a spectral energy distribution that is better described by leponic models instead of hadronic or large scale models. The details and implications of the VERITAS M87 result are presented in this dissertation

The High-Altitude water cherenkov (HAWC) observatory in México: The primary detector

The High-Altitude Water Cherenkov (HAWC) observatory is a second-generation continuously operated, wide field-of-view, TeV gamma-ray observatory. The HAWC observatory and its analysis techniques build on experience of the Milagro experiment in using ground-based water Cherenkov detectors for gamma-ray astronomy. HAWC is located on the Sierra Negra volcano in México at an elevation of 4100 meters above sea level. The completed HAWC observatory principal detector (HAWC) consists of 300 closely spaced water Cherenkov detectors, each equipped with four photomultiplier tubes to provide timing and charge information to reconstruct the extensive air shower energy and arrival direction. The HAWC observatory has been optimized to observe transient and steady emission from sources of gamma rays within an energy range from several hundred GeV to several hundred TeV. However, most of the air showers detected are initiated by cosmic rays, allowing studies of cosmic rays also to be performed. This paper describes the characteristics of the HAWC main array and its hardware.UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Físic