The SRG/eROSITA all-sky survey

First X-ray catalogues and data release of the western Galactic hemisphere^★

¹ Max-Planck-Institut fur Extraterrestrische Physik, Gieβenbachstraβe, 85748 Garching, Germany
e-mail: am@mpe.mpg.de
² Leibniz Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
³ Institut für Astronomie und Astrophysik, Universität Tubingen, Sand 1, 72076 Tübingen, Germany
⁴ Institute for Astronomy and Astrophysics, National Observatory of Athens, V. Paulou and I. Metaxa 11532, Greece
⁵ Exzellenzcluster ORIGINS, Boltzmannstr. 2, 85748 Garching, Germany
⁶ Dr. Karl Remeis-Sternwarte and Erlangen Centre for Astroparticle Physics, Friedrich-Alexander Universität Erlangen-Nurnberg, Sternwartstraβe 7, 96049 Bamberg, Germany
⁷ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
⁸ MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁹ Argelander Institute for Astronomy, University of Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
¹⁰ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
¹¹ Dipartimento di Fisica e Astronomia “Augusto Righi”, Università di Bologna, via Gobetti 93/2, 40129 Bologna, Italy
¹² INAF - Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Gobetti 93/3, 40129 Bologna, Italy
¹³ IRAP, Université de Toulouse, CNRS, UPS, CNES, Toulouse, France
¹⁴ Tautenburg Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
¹⁵ University Observatory Munich, Faculty of Physics, Ludwig-Maximilians-Universität, Scheinerstr. 1, 81679 Munich, Germany
¹⁶ Department of Physics & McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
¹⁷ Universität Innsbruck, Institut für Astro- und Teilchenphysik, Technikerstraβe 25/8, 6020 Innsbruck, Austria
¹⁸ TU Dresden, Institute of Nuclear and Particle Physics, 01062 Dresden, Germany
¹⁹ DESY, Notkestraβe 85, 22607 Hamburg, Germany
²⁰ Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637, USA
²¹ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
²² Istituto di Radioastronomia IRA-INAF, via Gobetti 101, 40129 Bologna, Italy
²³ INAF, Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, (LC), Italy
²⁴ Max-Planck Institut fur Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²⁵ CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei 230026, PR China
²⁶ School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, PR China

Received: 12 June 2023
Accepted: 26 November 2023

Abstract

The eROSITA telescope array aboard the Spektrum Roentgen Gamma (SRG) satellite began surveying the sky in December 2019, with the aim of producing all-sky X-ray source lists and sky maps of an unprecedented depth. Here we present catalogues of both point-like and extended sources using the data acquired in the first six months of survey operations (eRASS1; completed June 2020) over the half sky whose proprietary data rights lie with the German eROSITA Consortium. We describe the observation process, the data analysis pipelines, and the characteristics of the X-ray sources. With nearly 930 000 entries detected in the most sensitive 0.2–2.3 keV energy range, the eRASS1 main catalogue presented here increases the number of known X-ray sources in the published literature by more than 60%, and provides a comprehensive inventory of all classes of X-ray celestial objects, covering a wide range of physical processes. A smaller catalogue of 5466 sources detected in the less sensitive but harder 2.3–5 keV band is the result of the first true imaging survey of the entire sky above 2 keV. We present methods to identify and flag potential spurious sources in the catalogues, which we applied for this work, and we tested and validated the astrometric accuracy via cross-comparison with other X-ray and multi-wavelength catalogues. We show that the number counts of X-ray sources in eRASSl are consistent with those derived over narrower fields by past X-ray surveys of a similar depth, and we explore the number counts variation as a function of the location in the sky. Adopting a uniform all-sky flux limit (at 50% completeness) of F_{05–2 keV} > 5 × 10⁻¹⁴ erg s⁻¹ cm⁻², we estimate that the eROSITA all-sky survey resolves into individual sources about 20% of the cosmic X-ray background in the 1–2 keV range. The catalogues presented here form part of the first data release (DR1) of the SRG/eROSITA all-sky survey. Beyond the X-ray catalogues, DR1 contains all detected and calibrated event files, source products (light curves and spectra), and all-sky maps. Illustrative examples of these are provided.