CTAO Instrument Response Functions - Prod6 version v1.0

Overview The Cherenkov Telescope Array Observatory (CTAO) is the next-generation ground-based observatory for very-high-energy gamma-ray astronomy. Its two arrays are located at the Roque de los Muchachos Observatory on La Palma, Spain (CTAO-North), and at the Paranal Observatory in Chile (CTAO-South). They are designed to observe astrophysical gamma rays with energies from approximately 20 GeV to 300 TeV, with sensitivity and angular resolution substantially improved relative to current-generation gamma-ray observatories. As an open, proposal-driven observatory, CTAO will support a broad programme of research into cosmic particle acceleration, extreme astrophysical environments and fundamental physics. The dataset presented here contains Instrument Response Functions (IRFs) for the CTAO-North and CTAO-South Beta Configuration defined below. It provides ROOT and GADF-compatible FITS representations, together with a selection of performance figures corresponding to these IRFs. Array Beta Configurations The Beta Configuration uses Large-Sized Telescopes (LSTs), Medium-Sized Telescopes (MSTs), and Small-Sized Telescopes (SSTs) with the following layout: CTAO-North: 4 LSTs and 9 MSTs. CTAO-South: 2 LSTs, 14 MSTs, and 37 SSTs. Release Information IRF release: Prod6 v1.0 Publication: September 2026 Creator: Cherenkov Telescope Array Observatory Zenodo record: 22871179 DOI: https://doi.org/10.5281/zenodo.22871179 Contact: [e-mail] Licence: Creative Commons Attribution 4.0 International; see `LICENSE`. Citation and Acknowledgement When using these products, please cite the CTAO Prod6 v1.0 IRF Zenodo record (https://doi.org/10.5281/zenodo.22871179), CORSIKA [1], sim_telarray [5], the Prod6 telescope simulation model [6], Eventdisplay [7], and Eventdisplay-ML [8]. A BibTex file with the relevant references is provided alongside the data (`ctao_prod6_IRFs_citations.bib`). Suggested acknowledgement: This research has made use of the CTAO Prod6 instrument response functions, Prod6 v1.0, provided by the CTAO and archived at https://doi.org/10.5281/zenodo.22871179. Monte Carlo Simulations The response functions were derived from simulations using CORSIKA 7.750 [1, 2] with QGSJET-II-04 [3] for high-energy and URQMD [4] for low-energy hadronic interactions. Telescope response was simulated with `sim_telarray` release 2024.36.1 [5] using the CTAO Prod6 telescope simulation model [6]. The production includes gamma-ray, proton, and electron primary simulations. Nominal parallel telescope pointing is assumed. Simulations and derived products cover zenith angles of 20, 40, 52, and 60 degrees, with azimuth directions toward magnetic North and South and an azimuth-averaged response. Products are available for dark-sky conditions and for half-moon conditions, whose average sky-brightness level is five times the dark-sky level. Performance calculations assume a power-law gamma-ray spectrum with photon index 2.62. The proton background spectrum follows a fit to ATIC measurements [10, 11]. The electron background spectrum follows an internal fit to published Fermi-LAT, H.E.S.S., and MAGIC measurements [11-13]. Analysis and Performance Calculation Eventdisplay v5.17.0 [7], including the Eventdisplay-ML v1.0.0 stereo-reconstruction step [8], was used for reconstruction and response generation. The analysis is optimized for point-source flux sensitivity separately by energy bin and observing time: 100 s, 0.5 h, 5 h, and 50 h. Differential sensitivity requires a five-standard-deviation detection, at least ten detected gamma rays per energy bin, and signal-to-background ratio of at least 0.05. The standard energy binning uses five logarithmic bins per decade. Because the selections are optimized for flux sensitivity, these IRFs do not necessarily expose the best possible angular or energy resolution. Offset-dependent response products are provided where applicable. Azimuth-averaged IRFs are included for general studies. Instrument Response Functions The IRFs include effective area, residual background rate and energy and angular dispersion matrices. Differential sensitivity is provided in the ROOT files alongside energy and angular resolution curves, binned in off-axis angle. For each site, products cover 20, 40, 52, and 60 degree zenith angles, dark-sky and half-moon conditions, and North, South, and Azimuth-averaged response variants. The available exposure optimizations are 100 s, 0.5 h, 5 h, and 50 h. Data Formats ROOT products store the IRFs as histograms. FITS products are compatible with the Gamma-ray Astronomy Data Formats (GADF) specification [9] and can be used with compatible high-level science-analysis tools. Values are equivalent between formats except for the documented point-spread-function representation, where FITS uses a Gaussian approximation, whereas ROOT retains the fuller distribution. Package Organization Two downloadable bundles are provided: `ctao-prod6-zenodo-v1.0-fits-only/` contains the leaner FITS distribution for users who do not need ROOT products. `ctao-prod6-zenodo-v1.0/` contains both FITS and ROOT products. Both bundles contain a `LICENSE`, this description and a set of representative performance figures. The same FITS archives are present in both bundles. File Naming Convention Individual response files encode the production, array site, zenith angle, azimuth configuration, telescope layout, sky brightness condition, observing-time optimization, release version, and format. For example: `Prod6-CTAO-North-20deg-AverageAz-4LSTs09MSTs-dark-18000s-v1.0.fits.gz` `Prod6-CTAO-South-40deg-NorthAz-2LSTs14MSTs37SSTs-halfmoon-180000s-v1.0.root` Similar site, zenith and sky brightness conditions are bundled in tarballs, with the corresponding naming pattern `CTAO-Performance-Prod6-<site>-<zenith>-<condition>-v1.0.(ROOT/FITS).tar.gz`. Complete List of Distributed Archives The following FITS archives are included in both bundles: FITS `fits/CTAO-Performance-Prod6-CTAO-North-20deg-dark-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-North-20deg-halfmoon-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-North-40deg-dark-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-North-40deg-halfmoon-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-North-52deg-dark-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-North-52deg-halfmoon-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-North-60deg-dark-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-North-60deg-halfmoon-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-South-20deg-dark-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-South-20deg-halfmoon-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-South-40deg-dark-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-South-40deg-halfmoon-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-South-52deg-dark-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-South-52deg-halfmoon-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-South-60deg-dark-v1.0.FITS.tar.gz` `fits/CTAO-Performance-Prod6-CTAO-South-60deg-halfmoon-v1.0.FITS.tar.gz` ROOT The ROOT archives are supplied in the complete bundle only: `root/CTAO-Performance-Prod6-CTAO-North-20deg-dark-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-North-20deg-halfmoon-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-North-40deg-dark-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-North-40deg-halfmoon-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-North-52deg-dark-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-North-52deg-halfmoon-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-North-60deg-dark-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-North-60deg-halfmoon-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-South-20deg-dark-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-South-20deg-halfmoon-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-South-40deg-dark-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-South-40deg-halfmoon-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-South-52deg-dark-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-South-52deg-halfmoon-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-South-60deg-dark-v1.0.ROOT.tar.gz` `root/CTAO-Performance-Prod6-CTAO-South-60deg-halfmoon-v1.0.ROOT.tar.gz` Performance Figures and Archived Website `Performance_report_prod6.md` describes the supplied performance figures. For current information, use the CTAO performance page. References CORSIKA: A Monte Carlo code to simulate extensive air showers. Optimizing Cherenkov photons generation and propagation in CORSIKA for CTA Monte-Carlo simulations. QGSJET-II model. UrQMD: Relativistic Hadron-Hadron Collisions in the Ultra-Relativistic Quantum Molecular Dynamics Model. Bernloehr, K. 2008, Astroparticle Physics, 30, 149 (sim_telarray). CTAO Prod6 telescope simulation model. Eventdisplay: An Analysis and Reconstruction Package for Ground-based Gamma-ray Astronomy. Eventdisplay-ML: a machine learning toolkit for Eventdisplay. Gamma-ray Astronomy Data Formats (GADF). Guzik, T. G., et al. (1996), “The Advanced Thin Ionization Calorimeter (ATIC) Balloon Experiment: Instrumentation,” in Gamma-Ray and Cosmic-Ray Detectors, Techniques, and Missions, Proceedings of SPIE, 2806, 122. S. Swordy (personal communication). IFAE, 2013, internal fit to Fermi-LAT, H.E.S.S., and MAGIC measurements. Atwood, W. B., et al. (Fermi-LAT Collaboration), 2009, “The Large Area Telescope on the Fermi Gamma-Ray Space Telescope Mission,” The Astrophysical Journal, 697, 1071–1102. Aharonian, F., et al. (H.E.S.S. Collaboration), 2006, “Observations of the Crab Nebula with H.E.S.S.,” Astronomy & Astrophysics, 457, 899–915. Aleksić, J., et al. (MAGIC Collaboration), 2016, “The major upgrade of the MAGIC telescopes, Part II: A performance study using observations of the Crab Nebula,” Astroparticle Physics, 72, 76–94. Computing Acknowledgements We thank the computing centres that provided resources for the CTAO Prod6 IRFs: DESY-ZN, Deutsches Elektronen-Synchrotron, Standort Zeuthen, Germany INFN/INAF-FRASCATI, Frascati, Italy PIC, port d'informacio cientifica, Bellaterra, Spain Swiss National Supercomputing Centre (CSCS), Lugano, Switzerland Contact and Licence For support, contact `[e-mail]`. This dataset is released under the Creative Commons Attribution 4.0 International licence.