Background Measurements and Simulations of the ComPair Balloon Flight

TL;DR

This paper reports on the ComPair balloon flight, demonstrating its capabilities as a gamma-ray telescope, comparing measurements with simulations, and evaluating background rejection methods to inform future instrument development.

Contribution

It provides the first in-flight performance data of ComPair, validates simulation models, and assesses background rejection schemes for future gamma-ray observatories.

Findings

Good agreement between measurements and simulations.

Both background rejection schemes effectively reduced charged particle background.

Results support using the hard veto scheme for future flights.

Abstract

ComPair, a prototype of the All-sky Medium Energy Gamma-ray Observatory (AMEGO), completed a short-duration high-altitude balloon campaign on August 27, 2023 from Fort Sumner, New Mexico, USA. The goal of the balloon flight was the demonstration of ComPair as both a Compton and Pair telescope in flight, rejection of the charged particle background, and measurement of the background $\gamma$-ray spectrum. This analysis compares measurements from the balloon flight with Monte Carlo simulations to benchmark the instrument. The comparison finds good agreement between the measurements and simulations and supports the conclusion that ComPair accomplished its goals for the balloon campaign. Additionally, two charged particle background rejection schemes are discussed: a soft ACD veto that records a higher charged particle event rate but with less risk of event loss, and a hard ACD veto that limits the charged particle event rate on board. There was little difference in the measured spectra from the soft and hard ACD veto schemes, indicating that the hard ACD veto could be used for future flights. The successes of ComPair's engineering flight will inform the development of the next generation of ComPair with upgraded detector technology and larger active area.