Performance of a Small Array of Imaging Air Cherenkov Telescopes sited in Australia

TL;DR

This study evaluates the performance of a small array of Imaging Air Cherenkov Telescopes in Australia, showing that four medium-sized telescopes could effectively detect transient gamma-ray events and complement the CTA.

Contribution

It demonstrates the potential of a small MST-based IACT array in Australia for transient detection and complements CTA, based on detailed Monte Carlo simulations.

Findings

Larger telescope baselines improve angular resolution.

Higher altitude lowers energy thresholds.

A 4-telescope MST array can detect novae with high significance.

Abstract

As TeV gamma-ray astronomy progresses into the era of the Cherenkov Telescope Array (CTA), there is a desire for the capacity to instantaneously follow up on transient phenomena and continuously monitor gamma-ray flux at energies above $10^{12}$ eV. To this end, a worldwide network of Imaging Air Cherenkov Telescopes (IACTs) is required to provide triggers for CTA observations and complementary continuous monitoring. An IACT array sited in Australia would contribute significant coverage of the Southern Hemisphere sky. Here, we investigate the suitability of a small IACT array and how different design factors influence its performance. Monte Carlo simulations were produced based on the Small-Sized Telescope (SST) and Medium-Sized Telescope (MST) designs from CTA. Angular resolution improved with larger baseline distances up to 277m between telescopes, and energy thresholds were lower at 1000m altitude than at 0m. The $\sim$300 GeV energy threshold of MSTs proved more suitable for observing transients than the $\sim$1.2 TeV threshold of SSTs. An array of four MSTs at 1000m was estimated to give a 5.7$\sigma$ detection of an RS Ophiuchi-like nova eruption from a 4-hour observation. We conclude that an array of four MST-class IACTs at an Australian site would ideally complement the capabilities of CTA.