Search for diffuse cosmic gamma-ray flux using fractal and wavelet analysis from galactic region using single imaging Cerenkov telescopes

Abstract

We show from a simulations-based study of the TACTIC telescope that fractal and wavelet analysis of Cerenkov images, recorded in a single imaging Cerenkov telescope, enables almost complete segregation of isotropic gamma-ray initiated events from the overwhelming background of cosmic ray hadron-initiated events. This presents a new method for measuring galactic and extragalactic gamma-ray background above 1 TeV energy. Preliminary results based on this method are reported here. Primary aim is to explore the possibility of using data recorded by a single imaging atmospheric Cerenkov telescope ( IACT) for making accurate measurements of diffuse galactic and extragalactic gamma-ray flux above ∼1 TeV energy. Using simulated data of atmospheric Cerenkov images recorded in an IACT, initiated, both, by cosmic ray protons and diffuse gamma-rays with energies above 4 TeV and 2 TeV respectively, we identify the most efficient fractal/wavelet parameters of the recorded images for primary identification. The method is based on the pattern recognition technique and employs fractal and wavelet analysis of the recorded Cerenkov images for gamma-hadron segregation. We show that the value of wavelet dimension parameter B 6 can segregate Cerenkov images of hadronic origin from those of diffuse gamma-ray origin with almost 100% accuracy. We use the results to get a preliminary upper limit estimate of the diffuse galactic gamma-ray flux within galactic range of ∣ b∣ ⩽ −5° and ∣ l∣ ⩽ 200° above 2 TeV from a 36 h data set recorded by the TACTIC telescope.