Singular Templates of Imaging Cherenkov Shower distribution (STOICS): A background estimation method for very-high-energy γ -ray observations

Analyses of Imaging Atmospheric Cherenkov Telescope (IACT) data for extended γ -ray sources face the issue that the field of view does not offer sufficient regions for background estimations. In cases where the source angular size exceeds or occupies a significant part of the field of view, an independent background estimation method is necessary to carry out IACT analyses and to have a better understanding of the systematic uncertainties. The proposed new method utilizes Singular Value Decomposition to extract the low-dimension representations of the distribution of cosmic-ray events in OFF runs and uses cosmic-ray-like events in the ON runs to estimate the background of γ -like events. Using VERITAS archival data, we demonstrate that the new method is capable of providing reliable background modeling for observations across a wide range of observing conditions.