Singular Templates of Imaging Cherenkov Shower distribution (STOICS): A background estimation method for Very-High-Energy $\gamma$-ray observations

TL;DR

This paper introduces a novel background estimation method for Very-High-Energy gamma-ray observations using Singular Value Decomposition to improve analysis of extended sources in Imaging Atmospheric Cherenkov Telescope data.

Contribution

The paper presents a new SVD-based background estimation technique that effectively models cosmic-ray backgrounds in challenging observational scenarios.

Findings

Reliable background modeling demonstrated with VERITAS data.

Effective for sources occupying large parts of the field of view.

Applicable across diverse observing conditions.

Abstract

Analyses of Imaging Atmospheric Cherenkov Telescope (IACT) data for extended $\gamma$-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 $\gamma$-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.