The Cadmium Zinc Telluride Imager (CZTI) is a high energy, wide-field imaging instrument on AstroSat. CZTI's namesake Cadmium Zinc Telluride detectors cover an energy range from 20 keV to > 200 keV, with 11% energy resolution at 60 keV. The coded aperture mask attains an angular resolution of 17 over a 4• .6 × 4• .6 (FWHM) field of view. CZTI functions as an open detector above 100 keV, continuously sensitive to GRBs and other transients in about 30% of the sky. The pixellated detectors are sensitive to polarisation above ∼ 100 keV, with exciting possibilities for polarisation studies of transients and bright persistent sources. In this paper, we provide details of the complete CZTI instrument, detectors, coded aperture mask, mechanical and electronic configuration, as well as data and products.
The performance of the EAS array at Kolar Gold Fields (working since 1984 and upgraded by 1987) is described. The army has been designed lo seamh for sources of ulba high energy (UHE) photons. The array, the data recording and estimation of shower parameters are briefly described. The angular resolution of the array is discussed in derail. We demonsbate, using our data, that the shower front is not a plane and derive an expression for the correcrion lo be applied lo the observed time delays in each ms before fitting a plane front. We suggest using an accepmce cone, dependent on the number of timing detectors used to estimate lhe anival direction of ms, for pint source searches.
The nuniber distributions of Cerenkov photons seen by a mirror from pure eleclromagnetic cascades in the atmosphere initiated by very high-energy gamma rays are calculated. It is shown that the fluctuations of the number of these photons are not Poissonian, in general. It is also shown that the characteristics of the distribution depend on the distance of the mirror from the shower core. Significant correlations are observed between spatially separated mirrors. Also significant correlation is observed between the number distribution and the distribution of the shower maximum position. Differences in the nature of the number distributions and their correlations for different primary energies are discussed.
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