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

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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 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 observations show long term performance of the HAGAR telescopes. Based on about 219 hours of data, we report the detection of γ-rays from the Crab Nebula at a significance level of about 20σ, 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 detailed study of possible systematic effects in our analysis method on data taken with the HAGAR telescopes.

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Notes

  1. https://freestarcharts.com/messier-1

  2. Uncertainty in energy threshold is ±12 GeV

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Acknowledgements

We thank the engineering and technical staff of IIA and TIFR who have taken part in the construction, installation, maintenance of telescopes and data acquisition setup. Also, we thank the team at the HAGAR site for successful observations and data management. We also thank to Kevin Meagher and Markus Holler for providing VERITAS and HESS-II measurements of the Crab nebula.

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Authors and Affiliations

  1. Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005, India

    B. B. Singh, V. R. Chitnis, A. Sinha, B. S. Acharya, K. S. Gothe, B. K. Nagesh, S. K. Rao & S. S. Upadhya

  2. Indian Institute of Astrophysics, II Block, Koramangala, Bangalore, 560034, India

    A. Shukla, P. R. Vishwanath, G. C. Anupama, T. P. Prabhu & R. Srinivasan

  3. Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata, 700064, India

    L. Saha & P. Bhattacharjee

  4. Department of Physics, University of the Free State, PO Box 339, Bloemfontein, 9300, South Africa

    R. J. Britto

  5. Institute for Theoretical Physics and Astrophysics, Universität Würzburg, 97074, Würzburg, Germany

    A. Shukla

  6. Universidad de Complutense, E-28040, Madrid, Spain

    L. Saha

  7. Astroparticule et Cosmologie/CNRS/ Université Paris Diderot, Paris, 75013, France

    A. Sinha

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Singh, B.B., Britto, R.J., Chitnis, V.R. et al. VHE gamma-ray observation of Crab Nebula with HAGAR telescope array. Exp Astron 47, 177–198 (2019). https://doi.org/10.1007/s10686-019-09623-1

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