Analysis Methods for Gamma-ray Astronomy

TL;DR

This paper reviews analysis methods for gamma-ray astronomy, covering data formats, event reconstruction, and spectral analysis techniques used in Fermi-LAT and IACT observations, highlighting recent advancements and future prospects.

Contribution

It provides a comprehensive overview of analysis techniques in gamma-ray astronomy, including standard data formats, event reconstruction, and spectral extraction methods, with emphasis on recent developments.

Findings

Summarizes standard data formats for gamma-ray data

Details event reconstruction and selection algorithms

Describes high-level spectral analysis techniques

Abstract

The launch of the Fermi satellite in 2008, with its Large Area Telescope (LAT) on board, has opened a new era for the study of gamma-ray sources at GeV ($10^9$ eV) energies. Similarly, the commissioning of the third generation of imaging atmospheric Cherenkov telescopes (IACTs) - H.E.S.S., MAGIC, and VERITAS - in the mid-2000's has firmly established the field of TeV ($10^{12}$ eV) gamma-ray astronomy. Together, these instruments have revolutionised our understanding of the high-energy gamma-ray sky, and they continue to provide access to it over more than six decades in energy. In recent years, the ground-level particle detector arrays HAWC, Tibet, and LHAASO have opened a new window to gamma rays of the highest energies, beyond 100 TeV. Soon, next-generation facilities such as CTA and SWGO will provide even better sensitivity, thus promising a bright future for the field. In this chapter, we provide a brief overview of methods commonly employed for the analysis of gamma-ray data, focusing on those used for Fermi-LAT and IACT observations. We describe the standard data formats, explain event reconstruction and selection algorithms, and cover in detail high-level analysis approaches for imaging and extraction of spectra, including aperture photometry as well as advanced likelihood techniques.