Handling Systematic Uncertainties and Combined Source Analyses for Atmospheric Cherenkov Telescopes

TL;DR

This paper examines how systematic uncertainties affect atmospheric Cherenkov telescope data analysis, proposing a joint likelihood method that improves robustness and accuracy over traditional counting methods.

Contribution

It introduces a new joint likelihood technique to handle systematic uncertainties more effectively in atmospheric Cherenkov telescope analyses.

Findings

Traditional summation of ON and OFF counts can be misleading without proper calibration.

Erroneous estimates of systematic parameters lead to overestimated source significance.

The proposed joint likelihood method significantly improves analysis reliability.

Abstract

In response to an increasing availability of statistically rich observational data sets, the performance and applicability of traditional Atmospheric Cherenkov Telescope analyses in the regime of systematically dominated measurement uncertainties is examined. In particular, the effect of systematic uncertainties affecting the relative normalisation of fiducial ON and OFF-source sampling regions - often denoted as {\alpha} - is investigated using combined source analysis as a representative example case. The traditional summation of accumulated ON and OFF-source event counts is found to perform sub-optimally in the studied contexts and requires careful calibration to correct for unexpected and potentially misleading statistical behaviour. More specifically, failure to recognise and correct for erroneous estimates of {\alpha} is found to produce substantial overestimates of the combined population significance which worsen with increasing target multiplicity. An alternative joint likelihood technique is introduced, which is designed to treat systematic uncertainties in a uniform and statistically robust manner. This alternate method is shown to yield dramatically enhanced performance and reliability with respect to the more traditional approach.