Interpolation of Instrument Response Functions for the Cherenkov Telescope Array in the Context of pyirf

TL;DR

This paper evaluates various interpolation methods for Instrument Response Functions in the Cherenkov Telescope Array, enabling faster IRF estimation under different observation conditions using the pyirf software package.

Contribution

It introduces and compares multiple interpolation techniques for IRFs within the pyirf framework, specifically applied to the LST-1 prototype, improving efficiency in IRF generation.

Findings

Interpolation methods vary in accuracy and computational efficiency.

Specialized techniques are required for probability distribution components.

pyirf provides a flexible platform for IRF interpolation.

Abstract

The Cherenkov Telescope Array (CTA) will be the next generation ground-based very-high-energy gamma-ray observatory, constituted by tens of Imaging Atmospheric Cherenkov Telescopes at two sites once its construction and commissioning are finished. Like its predecessors, CTA relies on Instrument Response Functions (IRFs) to relate the observed and reconstructed properties to the true ones of the primary gamma-ray photons. IRFs are needed for the proper reconstruction of spectral and spatial information of the observed sources and are thus among the data products issued to the observatory users. They are derived from Monte Carlo simulations, depend on observation conditions like the telescope pointing direction or the atmospheric transparency and can evolve with time as hardware ages or is replaced. Producing a complete set of IRFs from simulations for every observation taken is a time-consuming task and not feasible when releasing data products on short timescales. Consequently, interpolation techniques on simulated IRFs are investigated to quickly estimate IRFs for specific observation conditions. However, as some of the IRFs constituents are given as probability distributions, specialized methods are needed. This contribution summarizes and compares the feasibility of multiple approaches to interpolate IRF components in the context of the pyirf python software package and IRFs simulated for the Large-Sized Telescope prototype (LST-1). We will also give an overview of the current functionalities implemented in pyirf.