Upgrading and testing the 3D reconstruction of gamma-ray air showers as observed with an array of Imaging Atmospheric Cherenkov telescopes

TL;DR

This paper enhances a 3D reconstruction method for gamma-ray air showers observed with Cherenkov telescopes, improving background rejection and validating the technique with real data, leading to more accurate gamma-ray measurements.

Contribution

The paper introduces an additional quality criterion to the existing 3D reconstruction method, significantly reducing background contamination while maintaining high gamma-ray efficiency.

Findings

Background contamination reduced by a factor of about 2.

Excellent agreement between data and simulations at a few percent level.

Validation of the 3D-reconstruction method with real blazar flare data.

Abstract

Stereoscopic arrays of Imaging Atmospheric Cherenkov Telescopes allow to reconstruct gamma-ray-induced showers in 3 dimensions, which offers several advantages: direct access to the shower parameters in space and straightforward calorimetric measurement of the incident energy. In addition, correlations between the different images of the same shower are taken into account. An analysis method based on a simple 3D-model of electromagnetic showers was recently implemented in the framework of the H.E.S.S. experiment. In the present article, the method is completed by an additional quality criterion, which reduces the background contamination by a factor of about 2 in the case of extended sources, while keeping gamma-ray efficiency at a high level. On the other hand, the dramatic flares of the blazar PKS 2155-304 in July 2006, which provided H.E.S.S. data with an almost pure gamma-ray sample, offered the unique opportunity of a precision test of the 3D-reconstruction method as well as of the H.E.S.S. simulations used in its calibration. An agreement at a few percent level is found between data and simulations for the distributions of all 3D shower parameters.