On the optimum spacing of stereoscopic imaging atmospheric Cherenkov telescopes

Abstract

For stereoscopic systems of imaging atmospheric Cherenkov telescopes (IACTs), a key parameter to optimize the sensitivity for VHE γ-ray point sources is the intertelescope spacing. Using pairs of telescopes of the HEGRA IACT system, the sensitivity of two-telescope stereo IACT systems is studied as a function of the telescope spacing, ranging from 70 m to 140 m. Data taken during the 1997 outburst of Mrk 501 are used to evaluate both the detection rates before cuts, and the sensitivity for weak signals after cuts to optimize the significance of signals. Detection rates decrease by about 1/3 between the minimum and maximum spacing. The significance of signals is essentially independent of distance, in the range investigated.

Design study of CANGAROO-III, stereoscopic imaging atmospheric Cherenkov telescopes for sub-TeV γ-ray detection

“…We studied the basic design parameters for the next three telescopes using the Monte Carlo technique. Similar studies have been carried out previously, for example by the VERITAS [3] and HESS [4] groups. We started from optimized parameters obtained by a previous study and our experience with CANGAROO-I, [1] and verified those results.…”

“…With a likelihood analysis and the above-mentioned camera design ("setup-2"), we proceeded to design a stereoscopic telescope system. Previous studies have investigated the effect of the telescope spacing [3] [4]. These indicated that a spacing within a range of 80 to 120 m is best.…”

Potential increased performance of an array of Cherenkov telescopes by means of their positioning using many-objective evolutionary optimizations

“…[20]). Considered as a function of one telescope depending on the impact parameter of observation 4 , the fluctuations L of the number of photoelectrons detected by a telescope are directly related to the energy resolution (e.g. [20]).…”

“…Thus their optimization has been figured out by finding via Monte Carlo simulations the best spacing among them in regular and symmetrical geometries and by optimizing the individual parameters of the telescopes (e.g. [4,5]). The spacing among the telescopes represents a trade-off between a good stereoscopic view of the showers and the requirement of a large effective area for good sensitivity.…”

“…The reflection in the telescope mirror of the Cherenkov radiation emitted by the shower print an image in the telescope camera in the form of an ellipse whose shape and orientation can be characterized by a set of parameters popularized by Hillas[19]. We are interested in two of these parameters: Size, which is the measure of the total number of photoelectrons recorded by the camera and Length, which is the root mean square of the distribution of the photoelectrons in the camera along the major axis of the ellipse that was fitted to the image 4. The impact parameter of observation is the radial distance of a telescope and the center of the shower.…”