The TACTIC atmospheric Cherenkov imaging telescope

Abstract

The TACTIC γ-ray telescope, equipped with a light collector of area ∼9.5m 2 and a medium resolution imaging camera of 349-pixels, has been in operation at Mt.Abu, India since 2001. This paper describes the main features of its various subsystems and its overall performance with regard to (a) tracking accuracy of its 2-axes drive system, (b) spot size of the light collector, (c) back-end signal processing electronics and topological trigger generation scheme, (d) data acquisition and control system and (e) relative and absolute gain calibration methodology. Using a trigger field of view of 11×11 pixels (∼ 3.4 • ×3.4 • ), the telescope records a cosmic ray event rate of ∼2.5 Hz at a typical zenith angle of 15 • . Monte Carlo simulation results are also presented in the paper for comparing the expected performance of the telescope with actual observational results. The consistent detection of a steady signal from the Crab Nebula above ∼1.2 TeV energy, at a sensitivity level of ∼5.0σ in ∼25 h, alongwith excellent matching of its energy spectrum with that obtained by other groups, reassures that the performance of the TACTIC telescope is quite stable and reliable. Furthermore, encouraged by the detection of strong γ-ray signals from Mrk 501 (during 1997(during and 2006(during observations) and Mrk 421 (during 2001(during and 2005(during -2006 observations), we believe that there is considerable scope for the TACTIC telescope to monitor similar TeV γ-ray emission activity from other active galactic nuclei on a long term basis.

Very high energy γ-ray observations of Mrk 501 using the TACTIC imaging γ-ray telescope during 2005–06

“…The data acquisition and control system of the telescope [22] has been designed around a network of PCs running the QNX real-time operating system. The details of the telescope functioning are presented elsewhere [12]. The telescope is sensitive to γ-rays above 1 TeV and can detect the Crab Nebula at 5σ significance level in 25 hours of ON source observation.…”

Multiwavelength study of VHE emission from Markarian 501 using TACTIC observations during April–May, 2012

“…The safe anode current (3µA) operation of the PMT has been ensured by implementing a gain control algorithm [28]. The detailed description of the telescope related hardware and software can be found in [29,30].…”

Ground-based TeV γ-ray Astronomy in India - Historical Perspective and Recent Developments

“…The telescope has a pointing and tracking accuracy of better than 3'. The details of the various subsystems of the telescope are discussed in [30,31,32,33].…”