# VHE Gamma-ray Observation of Crab Nebula with HAGAR Telescope Array

## TL;DR

This paper reports a nine-year observational study of the Crab Nebula using the HAGAR atmospheric Cherenkov telescope array, detecting gamma-ray emissions above 230 GeV with high significance and analyzing systematic effects.

## Contribution

First long-term performance assessment of the HAGAR telescopes with gamma-ray detection from Crab Nebula over nine years.

## Key findings

- Detected gamma rays from Crab Nebula at 20σ significance
- Measured average flux of (1.64±0.09)×10^{-10} photons cm^{-2} sec^{-1} above 230 GeV
- Analyzed systematic effects impacting the observational data

## Abstract

HAGAR is a system of seven Non-imaging Atmospheric Cherenkov Telescopes located at Hanle in the Ladakh region of the Indian Himalayas at an altitude of 4270 meters {\it 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 $\gamma$-ray signal amidst cosmic ray background. The consolidated results spanning nine years of the Crab nebula observations show long term performance of the HAGAR telescopes. Based on about 219 hours of data, we report the detection of $\gamma$-rays from the Crab Nebula at a significance level of about 20$\sigma$, corresponding to a time averaged flux of (1.64$\pm$0.09) $\times10^{-10}$ photons cm$^{-2}$ sec$^{-1}$ above 230 GeV. Also, we perform a detailed study of possible systematic effects in our analysis method on data taken with the HAGAR telescopes.