Observations with the High Altitude GAmma-Ray (HAGAR) telescope array in the Indian Himalayas
1Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India
2Indian Institute of Astrophysics, Sarjapur Road, 2nd Block, Koramangala, Bangalore 560034, India
3Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
4Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700 064, India
5Now at Washington University, St Louis, MO 63130, USA
Abstract. The High Altitude GAmma-Ray (HAGAR) array is a wavefront sampling array of 7 telescopes, set-up at Hanle, at 4270 m amsl, in the Ladakh region of the Himalayas (Northern India). It constitutes the first phase of the HImalayan Gamma-Ray Observatory (HIGRO) project. HAGAR is the first array of atmospheric Cherenkov telescopes established at a so high altitude, and was designed to reach a relatively low threshold (currently around 200 GeV) with quite a low mirror area (31 m2). Regular source observations are running since September 2008. Estimation of the sensitivity of the experiment is undergoing using several hours of data from the direction of Crab nebula, the standard candle source of TeV gamma-ray astronomy, and from dark regions. Data were acquired using the On-source/Off-source tracking mode, and by comparing these sky regions the strength of the gamma-ray signal could be estimated. Gamma-ray events arrive close to telescope axis direction while the cosmic-ray background events arrive from the whole field of view. We discuss our analysis procedures for the estimate of arrival direction, estimate of gamma ray flux from Crab nebula, and the sensitivity of the HAGAR system, in this paper.