Bhat, P. N.

B. S. Acharya, V. R. Chitnis, P. Mazumdar, M. A. Rahman, M. R. Krishnaswamy and P. R. Vishwanath


Pachmarhi Array of Cerenkov Telescopes (PACT) has been designed to search for TeV  g- rays using the wavefront sampling technique. PACT consists of 25 telescopes deployed over an area of 80 m×100 m, while each telescopes consists of 7 parabolic reflectors with a fast phototube behind a 3 (FWHM) mask at the focus of each of them. Photon density and arrival time (correct to a quarter of a nanosecond) are measured at six of the seven mirrors. The energy threshold and collection area of the array are estimated from a Monte Carlo technique using the measured event rate to be ~ 1  TeV and 105 m2 respectively. Recent engineering runs taken from this array enable us to calculate the accuracy by which arrival angle for a near vertical shower can be estimated to be 0.1 around the threshold energy. This could deteriorate to ~ 0.12 for showers at around 30. The limiting angular accuracy will improve with increasing primary energy because of the increased number of degrees of freedom. The sensitivity of the array for a 5s detection of g-ray signal has been estimated to be ~ 4.1×10-12  photons cm-2 s-1, for an on source exposure of 50 hrs. While calculating this it is asumed that 99.75% of the off-axis hadronic events could be rejected from directional information and nearly 75% of the on-axis hadronic events could be rejected using species sensitive measurements like the photon density fluctuations. In addition, it is assumed that ~ 66% of the g-rays are lost in the hadron rejection process. Consequently, the continuum emission from the Crab nebula could be detected at 5s level during an on-source exposure of 4 hours.

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On 23 Aug 1999, 11:46.