Effect of the uncertainty in the hadronic interaction models on the estimation of the sensitivity of the Cherenkov telescope array

Michiko Ohishi,Luisa Arrabito,Vitor De Souza,Konrad Bernlöhr,Johan Bregeon,Abelardo Moralejo Olaizola,Luan Arbeletche,Takanori Yoshikoshi,Gernot Maier

doi:10.1088/1361-6471/abfce0

Abstract

Imaging atmospheric Cherenkov telescopes (IACTs) are ground-based indirect detectors for cosmic gamma rays with energies above tens of GeV. The major backgrounds for gamma-ray observations in IACTs are cosmic-ray charged particles. The capability to reject these backgrounds is the most important factor determining the gamma-ray sensitivity of IACT systems. Monte Carlo simulations are used to estimate the residual background rates and sensitivity of the systems during the design and construction phase. Uncertainties in the modeling of high-energy hadronic interactions of cosmic rays with nuclei in the air propagate into the estimates of residual background rates and subsequently into the estimated instrument sensitivity. We investigate the influence of the difference in the current hadronic interaction models on the estimated gamma-ray sensitivity of the Cherenkov Telescope Array using four interaction models (QGSJET-II-03, QGSJET-II-04, EPOS-LHC, and SIBYLL2.3c) implemented in the air shower simulation tool CORSIKA. Variations in background rates of up to a factor 2 with respect to QGSJET-II-03 are observed between the models, mainly due to differences in the π 0 production spectrum. These lead to ∼30% differences in the estimated gamma-ray sensitivity in the 1–30 TeV region, assuming a 50 h observation of a gamma-ray point-like source. The presented results also show that IACTs have a significant capability in the verification of hadronic interaction models.

Highlights

Indirect cosmic ray detectors play an essential role in the observations of very-high-energy (VHE, 1011–1014 eV) and ultra-high-energy (>1014 eV) cosmic gamma rays
We investigate the influence of the difference in the current hadronic interaction models on the estimated gammaray sensitivity of the Cherenkov Telescope Array using four interaction models (QGSJET-II-03, QGSJET-II-04, EPOS-large hadron collider (LHC), and SIBYLL2.3c) implemented in the air shower simulation tool CORSIKA
It is expected from these features that EPOS-LHC and SIBYLL2.3c will produce more gamma-like background events than the two QGSJET-II models at energies around 1 TeV

Summary

Introduction

Indirect cosmic ray detectors play an essential role in the observations of very-high-energy (VHE, 1011–1014 eV) and ultra-high-energy (>1014 eV) cosmic gamma rays Their large collection area (>104 m2) is achieved by utilizing the extensive air shower (EAS) phenomena induced by the primary cosmic ray hitting the atmosphere. Hadronic showers induced by cosmic ray protons and heavier nuclei include EM showers as sub-structures, originated primarily from neutral pion (π0) decay. Those sub-EM showers can mimic showers from gamma rays in IACT observations [4,5,6,7]. IACT systems do not achieve background-free gammaray observations and the amount of residual cosmic ray events is the most important factor determining the gamma-ray sensitivity of an IACT system

Results

Discussion

Conclusion