PACHMARHI ARRAY OF CERENKOV TELESCOPES
Bhat, P. N.
B. S. Acharya, V. R. Chitnis, P. Mazumdar,
M. A. Rahman, M. R. Krishnaswamy and P. R. Vishwanath
Abstract
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.
File translated from TEX by TTH, version 2.32.
On 23 Aug 1999, 11:46.