| Description |
The matched-runs method of performing high-resolution imaging of extended very high-energy (VHE, E>100 GeV) γ-ray sources using the Very Energetic Radiation Imaging Telescope Array System (VERITAS) is characterized in this study. Several extended VHE γ-ray sources have been detected by the Milagro and High-Altitude Water Cherenkov (HAWC) gamma-ray detectors. However, due to the poor spatial and energy resolution of these detectors, the detail of the measurements is are limited. VERITAS is an Imaging Air Cherenkov Telescope (IACT) with better spatial and energy resolution than Milagro and HAWC. However, the spatial extent of these sources is comparable to the field of view (FOV) of VERITAS. Therefore, it is difficult to find a background region for estimating the cosmic ray background in images of extended sources. A new method of image analysis, called the matched-runs method, provides promise for analysing these images in detail. The matched-runs method involves comparing these extended γ-ray sources with images of known point-like sources taken under similar conditions as the images of the extended sources. In this study, the matched-runs method is characterized by determining the response of several parameters on the analysis of images of a known source, the Crab Nebula. In this analysis, several images of the Crab Nebula taken in different days are matched against a reference image of the Crab Nebula taken in 2011. An analysis of the effects of several observational conditions on the quality of the image is done by comparing the image from the matched-runs analysis on an image generating using a standard analysis. Preliminary results show no significant direct correlation of any one of the aforementioned parameters on the quality of the image, other than the absolute number of days between the background run observation and the source run observation. Therefore, a possible external factor concerning long-term changes in the telescope performance may be at play here, such as slow changes in mirror reflectivity or optical alignment. |
