The topological second-level trigger of the H.E.S.S. phase 2 telescope

TL;DR

This paper presents the design, implementation, and evaluation of a second-level trigger system for the H.E.S.S. phase 2 telescope, aimed at reducing false triggers during monoscopic observations in gamma-ray astronomy.

Contribution

It introduces a novel hardware-based second-level trigger system specifically for the H.E.S.S. phase 2 telescope, enhancing its ability to suppress spurious triggers in monoscopic mode.

Findings

The trigger system effectively reduces false triggers during monoscopic operation.

Hardware implementation achieves real-time processing with expected high performance.

The system's performance is validated through simulations and prototype testing.

Abstract

H.E.S.S is an array of atmospheric Cherenkov telescopes dedicated to GeV-TeV gamma-ray astronomy. The original array has been in operation since the beginning of 2004. It is composed of four 12-meter diameter telescopes. The installation of a fifth 28-meter diameter telescope is being completed. This telescope will operate both in stereoscopic mode and in monoscopic mode i.e. without a coincident detection on the smaller telescopes. A second-level trigger system is needed to supress spurious triggers of the 28-meter telescope when operated in monoscopic mode. This paper gives the motivation and principle of the second-level trigger. The principle of operation is illustrated by an example algorithm. The hardware implementation of the second level trigger system of H.E.S.S. phase 2 is described and its expected performances are then evaluated.