Significance for signal changes in gamma-ray astronomy

TL;DR

This paper introduces a simple, exposure-independent method for assessing the significance and stability of gamma-ray signals, effectively accounting for photon count fluctuations and systematic uncertainties.

Contribution

It proposes a new criterion for testing the constancy of gamma-ray sources, improving real-time evaluation of signal stability in gamma-ray astronomy.

Findings

Method effectively detects intensity changes in gamma-ray sources.

Demonstrated on real data from high-energy gamma-ray telescopes.

Identified some measurements as statistically significant variations.

Abstract

We describe a straightforward modification of frequently invoked methods for the determination of the statistical significance of a gamma-ray signal observed in a counting process. A simple criterion is proposed to decide whether a set of measurements of the numbers of photons registered in the source and background regions is consistent with the assumption of a constant source activity. This method is particularly suitable for immediate evaluation of the stability of the observed gamma-ray signal. It is independent of the exposure estimates, reducing thus the impact of systematic inaccuracies, and properly accounts for the fluctuations in the number of detected photons. The usefulness of the method is demonstrated on several examples. We discuss intensity changes for gamma-ray emitters detected at very high energies by the current gamma-ray telescopes (e.g. 1ES 0229+200, 1ES 1959+650 and PG 1553+113). Some of the measurements are quantified to be exceptional with large statistical significances.