Towards open and reproducible multi-instrument analysis in gamma-ray astronomy

¹ DESY, Platanenallee 6, 15738 Zeuthen, Germany
e-mail: cosimo.nigro@desy.de
² Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany
³ Landessternwarte, Universität Heidelberg, Königstuhl, 69117 Heidelberg, Germany
⁴ Instituto de Astrofísica de Andalucía – CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁵ Unidad de Partículas y Cosmología (UPARCOS), Universidad Complutense, 28040 Madrid, Spain
⁶ APC, AstroParticule et Cosmologie, Université Paris Diderot, CNRS/IN2P3, CEA/Irfu, Observatoire de Paris, Sorbonne Paris Cité, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France
⁷ TU Dortmund, Astroteilchenphysik E5b, 44227 Dortmund, Deutschland
⁸ Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
⁹ Physics Department, McGill University, Montreal, QC H3A 2T8, Canada
¹⁰ Institut de Astrofísica d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology (BIST), 08193 Bellaterra, Barcelona, Spain
¹¹ LUTH, Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, 5 Place Jules Janssen, 92190 Meudon, France
¹² IRFU, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France

Received: 20 December 2018
Accepted: 14 March 2019

Abstract

The analysis and combination of data from different gamma-ray instruments involves the use of collaboration proprietary software and case-by-case methods. The effort of defining a common data format for high-level data, namely event lists and instrument response functions (IRFs), has recently started for very-high-energy gamma-ray instruments, driven by the upcoming Cherenkov Telescope Array (CTA). In this work we implemented this prototypical data format for a small set of MAGIC, VERITAS, FACT, and H.E.S.S. Crab nebula observations, and we analyzed them with the open-source gammapy software package. By combining data from Fermi-LAT, and from four of the currently operating imaging atmospheric Cherenkov telescopes, we produced a joint maximum likelihood fit of the Crab nebula spectrum. Aspects of the statistical errors and the evaluation of systematic uncertainty are also commented upon, along with the release format of spectral measurements. The results presented in this work are obtained using open-access on-line assets that allow for a long-term reproducibility of the results.