Gammapy: A Python package for gamma-ray astronomy

¹ Center for Astrophysics | Harvard and Smithsonian, USA
e-mail: gammapy-coordination-l@in2p3.fr
² Université de Paris Cité, CNRS, Astroparticule et Cosmologie, 75013 Paris, France
³ Max-Planck-Institut für Kernphysik, PO Box 103980, 69029 Heidelberg, Germany
⁴ IPARCOS Institute and EMFTEL Department, Universidad Complutense de Madrid, 28040 Madrid, Spain
⁵ Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology, Campus UAB, Bellaterra, 08193 Barcelona, Spain
⁶ INAF/IASF Palermo, Via U. La Malfa, 153, 90146 Palermo PA, Italy
⁷ Instituto de Astrofísica de Andalucia-CSIC, Glorieta de la Astronomia s/n, 18008 Granada, Spain
⁸ Point 8 GmbH Rheinlanddamm 201, 44139 Dortmund, Germany
⁹ Astroparticle Physics, Department of Physics, TU Dortmund University, Otto-Hahn-Str. 4a, 44227 Dortmund, Germany
¹⁰ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
¹¹ Departament de Física Quàntica i Astrofísica (FQA), Universitat de Barcelona (UB), c. Martí i Franqués, 1, 08028 Barcelona, Spain
¹² Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB), c. Martí i Franqués, 1, 08028 Barcelona, Spain
¹³ Institut d’Estudis Espacials de Catalunya (IEEC), c. Gran Capità, 2-4, 08034 Barcelona, Spain
¹⁴ Departament de Física Quàntica i Astrofísica, Institut de Ciències del Cosmos, Universitat de Barcelona, IEEC-UB, Martí i Franquès, 1, 08028 Barcelona, Spain
¹⁵ Deutsches Elektronen-Synchrotron (DESY), 15738 Zeuthen, Germany
¹⁶ Institute of physics, Humboldt-University of Berlin, 12489 Berlin, Germany
¹⁷ Université Savoie Mont-Blanc, CNRS, Laboratoire d’Annecy de Physique des Particules - IN2P3, 74000 Annecy, France
¹⁸ Max Planck Institute for extraterrestrial Physics, Giessenbachstrasse, 85748 Garching, Germany
¹⁹ Laboratoire Univers et Théories, Observatoire de Paris, Université PSL, Université Paris Cité, CNRS, 92190 Meudon, France
²⁰ Max Planck Computing and Data Facility, Gießenbachstraße 2, 85748 Garching, Germany
²¹ School of Physics, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein, Johannesburg 2050, South Africa
²² The Hong Kong University of Science and Technology, Department of Electronic and Computer Engineering, PR China
²³ Cherenkov Telescope Array Observatory gGmbH (CTAO gGmbH) Saupfercheckweg 1, 69117 Heidelberg, Germany
²⁴ Erlangen Centre for Astroparticle Physics (ECAP), Friedrich-Alexander-Universität Erlangen-Nürnberg, Nikolaus-Fiebiger Strasse 2, 91058 Erlangen, Germany
²⁵ IRFU, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
²⁶ Stocadro GmbH Arthur-Hoffmann-Straße 95, 04275 Leipzig, Germany
²⁷ Meteo France International, 31100 Toulouse, France
²⁸ Université Bordeaux, CNRS, LP2I Bordeaux, UMR 5797 France
²⁹ Sorbonne Université, Université Paris Diderot, Sorbonne Paris Cité, CNRS/IN2P3, Laboratoire de Physique Nucléaire et de Hautes Energies, LPNHE, 4 Place Jussieu, 75252 Paris, France
³⁰ Academic Computer Centre Cyfronet, AGH University of Science and Technology, Krakow, Poland
³¹ Caltech/IPAC, MC 100-22, 1200 E. California Boulevard, Pasadena, CA 91125, USA
³² Institut für Astro- und Teilchenphysik, Leopold-Franzens-Universität Innsbruck, 6020 Innsbruck, Austria

Received: 23 March 2023
Accepted: 7 July 2023

Abstract

Context. Traditionally, TeV-γ-ray astronomy has been conducted by experiments employing proprietary data and analysis software. However, the next generation of γ-ray instruments, such as the Cherenkov Telescope Array Observatory (CTAO), will be operated as open observatories. Alongside the data, they will also make the associated software tools available to a wider community. This necessity prompted the development of open, high-level, astronomical software customized for high-energy astrophysics.

Aims. In this article, we present Gammapy, an open-source Python package for the analysis of astronomical γ-ray data, and illustrate the functionalities of its first long-term-support release, version 1.0. Built on the modern Python scientific ecosystem, Gammapy provides a uniform platform for reducing and modeling data from different γ-ray instruments for many analysis scenarios. Gammapy complies with several well-established data conventions in high-energy astrophysics, providing serialized data products that are interoperable with other software packages.

Methods. Starting from event lists and instrument response functions, Gammapy provides functionalities to reduce these data by binning them in energy and sky coordinates. Several techniques for background estimation are implemented in the package to handle the residual hadronic background affecting γ-ray instruments. After the data are binned, the flux and morphology of one or more γ-ray sources can be estimated using Poisson maximum likelihood fitting and assuming a variety of spectral, temporal, and spatial models. Estimation of flux points, likelihood profiles, and light curves is also supported.

Results. After describing the structure of the package, we show, using publicly available gamma-ray data, the capabilities of Gammapy in multiple traditional and novel γ-ray analysis scenarios, such as spectral and spectro-morphological modeling and estimations of a spectral energy distribution and a light curve. Its flexibility and its power are displayed in a final multi-instrument example, where datasets from different instruments, at different stages of data reduction, are simultaneously fitted with an astrophysical flux model.