Observations of high energy emission from pulsar wind nebulae using VERITAS

Broadband emission has been detected from several pulsar wind nebulae (PWNe), however the physical processes that govern the dynamics and mechanisms for the emission are not well understood. Theoretical models have been developed to attempt to explain the emission seen from these objects, and they make specific predictions about the spectrum and luminosity that we can expect to see in various wavelengths. Apparently, PWNe are thought to be strong gamma ray emitters, and this is reinforced by the strong emission seen from the Crab nebula. However, observations of other PWNe in high energy gamma rays has only recently been undertaken. VERITAS (the Very Energetic Radiation Imaging Telescope Array System) recently observed several of these sources in an attempt to detect very high energy gamma rays created in their nebulae. Results of observations of the Crab nebula, the standard source of observation for ground based gamma ray observatories and the most studied of all PWNe, are reported here as a comparison for 4 other northern hemisphere PWNe that were observed. This work will describe the nature of these objects while outlining the work being done to describe the emission detected from various sources. The technical details of the analysis techniques employed to search for high energy gamma rays using the VERITAS array is also presented. Ultimately only the Crab Nebula was detected at high significance. However the best integral flux upper-limits above 250 GeV to date are determined for 3C 58 (1.6% Crab Nebula flux), the Boomerang Nebula (1.5% Crab Nebula flux), PSR J0631+1036 (2.1% Crab Nebula flux) and PSR J1930+1852 (3.7 % Crab Nebula flux)