Artificial Neural Network based [formula omitted] segregation methodology for TACTIC telescope

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 γ-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 γ/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 ∼101.44h of Crab Nebula data collected by the TACTIC telescope, during November 10, 2005–January 30, 2006, yields an excess of ∼(1141±106) with a statistical significance of ∼11.07σ, as against an excess of ∼(928±100) with a statistical significance of ∼9.40σ 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 ∼1–24TeV.