Possible discrimination between gamma rays and hadrons using Čerenkov photon timing measurements

Abstract

AtmosphericČerenkov Technique is an established methodology to study T eV energy gamma rays. However the challenging problem has always been the poor signal to noise ratio due to the presence of abundant cosmic rays. Several ingenious techniques have been employed to alleviate this problem, most of which are centred around theČerenkov image characteristics. However there are not many techniques available for improving the signal to noise ratio of the data from wavefront sampling observations. One such possible technique is to use theČerenkov photon arrival times and identify the species dependent characteristics in them. Here we carry out systematic monte carlo simulation studies of the timing information ofČerenkov photons at the observation level. We have parameterized the shape of theČerenkov shower front as well as the pulse shapes in terms of experimentally measurable quantities. We demonstrate the sensitivity of the curvature of the shower front, pulse shape parameters as well as the photon arrival time jitter to primary species and show their efficiency in improving the signal to noise ratio. The effect of limiting theČerenkov telescope opening angle by using a circular focal point mask, on the efficacy of the parameters has also been studied for each of the parameters. Radius of the shower front, pulse decay time and photon arrival time jitter have been found to be the most promising parameters which could be used to discriminate γ−ray events from the background. We also find that the efficiency of the first two parameters increases with zenith angle and efficiency of pulse decay time decreases with increasing altitude of observation.

Angular resolution of the Pachmarhi array of Čerenkov telescopes

“…The corresponding values are shown in table 2. These values are comparable to the intrinsic timing jitter for proton primaries estimated from simulation studies for PACT telescopes [15]. This means that the contribution to timing resolution from instrumental effects is negligibly small.…”

“…The data used for estimating the angular resolution of PACT reported here consists of cosmic rays. It is well known that the protons exhibit a larger (by almost a factor of 4) intrinsic timing jitter relative to γ-ray primaries [15]. While the contribution of systematic effects to the timing resolution (which is estimated to be small) is independent of the primary species, the decreased intrinsic timing jitter is expected to improve the angular resolution for γ-ray primaries significantly.…”

FADC signal reconstruction for the MAGIC telescope

“…Since air showers from hadronic cosmic rays trigger the telescope much more frequently than γ-ray showers, the reconstructed pulse shape of the cosmic events corresponds mainly to hadron induced showers. The pulse shape from electromagnetic air showers might be slightly different as indicated by MC simulations [3,18]. The pulse shape for green calibration LED pulses is wider and has a pronounced tail.…”

“…Monte Carlo (MC) based simulations predict different time structures for γ-ray and hadron induced shower images as well as for images of single muons [3,18,28,31]. This has two consequences: On the one hand the arrival time structures across the observed Cherenkov shower image, from pixel to pixel, depend on the type of the primary particle.…”

Very high-energy γ-ray observations of the Crab nebula and other potential sources with the GRAAL experiment

“…It is well known that the arrival times in proton-induced showers have a much wider scatter around the mean arrival time than in gamma-induced showers due to their more irregular development in the atmosphere [19]. The experimental determination of this scatter has been proposed to be an efficient method for gamma/hadron separation [20]. Fig.13b.…”