VHE gamma-ray observation of Crab Nebula with HAGAR telescope array

Abstract

HAGAR is a system of seven Non-imaging Atmospheric Cherenkov Telescopes located at Hanle in the Ladakh region of the Indian Himalay as at an altitude of 4270 meters amsl . Since 2008, we have observed the Crab Nebula to assess the performance of the HAGAR telescopes. We describe the analysis technique for the estimation of γ -ray signal amidst cosmic ray background. The consolidated results spanning nine years of the Crab nebula obs ervations show long term performance of the HAGAR telescopes. Based on ab out 219 hours of data, we report the detection of γ -rays from the Crab Nebula at a significance level of about 20 σ , corresponding to a time averaged flux of (1.64 ± 0.09) × 10 − 10 photons cm − 2 sec − 1 above 230 GeV. Also, we perform a 2 B.B. Singh et al. detailed study of possible systematic effects in our analysis method o n data taken with the HAGAR telescopes.