Artificial Neural Network based gamma-hadron segregation methodology for TACTIC telescope

TL;DR

This paper evaluates various artificial neural network algorithms for gamma-hadron separation in Cherenkov telescope data, finding the Levenberg-Marquardt method most effective, leading to improved detection significance and energy spectrum analysis of the Crab Nebula.

Contribution

The study systematically compares ANN algorithms for gamma-hadron segregation, identifying the Levenberg-Marquardt method as superior for Cherenkov telescope data analysis.

Findings

Levenberg-Marquardt outperforms other ANN algorithms in segregation accuracy.

ANN method yields higher significance detection of Crab Nebula signals.

Re-determined Crab Nebula energy spectrum in 1-24 TeV range using ANN.

Abstract

The sensitivity of a Cherenkov imaging telescope is strongly dependent on the rejection of the cosmic-ray background events. The methods which have been used to achieve the segregation between the gamma-rays from the source and the background cosmic-rays, include methods like Supercuts/Dynamic Supercuts, Maximum likelihood classifier, Kernel methods, Fractals, Wavelets and random forest. While the segregation potential of the neural network classifier has been investigated in the past with modest results, the main purpose of this paper is to study the gamma / hadron segregation potential of various ANN algorithms, some of which are supposed to be more powerful in terms of better convergence and lower error compared to the commonly used Backpropagation algorithm. The results obtained suggest that Levenberg-Marquardt method outperforms all other methods in the ANN domain. Applying this ANN algorithm to $\sim$ 101.44 h of Crab Nebula data collected by the TACTIC telescope, during Nov. 10, 2005 - Jan. 30, 2006, yields an excess of $\sim$ (1141$\pm$106) with a statistical significance of $\sim$ 11.07$\sigma$, as against an excess of $\sim$ (928$\pm$100) with a statistical significance of $\sim$ 9.40$\sigma$ obtained with Dynamic Supercuts selection methodology. The main advantage accruing from the ANN methodology is that it is more effective at higher energies and this has allowed us to re-determine the Crab Nebula energy spectrum in the energy range $\sim$ 1-24 TeV.