BlazEr1: The eROSITA blazar catalog

Blazars and blazar candidates in the first eROSITA survey

¹ Dr. Karl Remeis-Sternwarte and Erlangen Centre for Astroparticle Physics, Friedrich-Alexander Universität Erlangen-Nürnberg, Sternwartstr. 7, 96049 Bamberg, Germany
² Department of Physics & McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
³ Department of Physics and Astronomy, Bowdoin College, Brunswick, ME 04011, USA
⁴ Deutsches Elektronen-Synchrotron DESY, Platanenallee 6, 15738 Zeuthen, Germany
⁵ Department of Physics and Astronomy, Clemson University, Clemson, SC 29631, USA
⁶ Max-Planck-Institut für extraterrestrische Physik, Gießenbachstraße 1, 85748 Garching, Germany
⁷ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁸ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
⁹ INAF – Osservatorio di Astrofisica e Scienza dello Spazio, via Gobetti 93/3, 40129 Bologna, Italy
¹⁰ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹¹ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
¹² Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹³ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716 Warsaw, Poland
¹⁴ Julius-Maximilians-Universität Würzburg, Fakultät für Physik und Astronomie, Institut für Theoretische Physik und Astrophysik, Lehrstuhl für Astronomie, Emil-Fischer-Str. 31, 97074 Würzburg, Germany
¹⁵ Max-Planck-Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
¹⁶ GFZ Helmholtz Centre for Geosciences, Telegrafenberg, 14476 Potsdam, Germany
¹⁷ NASA HQ, 300 E St. SW, DC 20546-0002 Washington, DC, USA

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 27 October 2025
Accepted: 4 March 2026

Abstract

Aims.eROSITA, on board the Spectrum Roentgen Gamma (SRG) spacecraft, performed its first X-ray all-sky survey (eRASS1) between December 2019 and June 2020. It detected about 930 000 sources, providing us with an unprecedented opportunity for a detailed blazar census properties of blazars and blazar candidates in eRASS1 and the compilation of the eROSITA blazar catalog.

Methods. We compiled a list of blazar and blazar candidates from the literature and matched it with the eRASS1 catalog, constructing the Blazars in eRASS1 (BlazEr1) catalog. For sources with more than 50 counts, we obtained their X-ray spectral properties. We compiled multiwavelength data from the radio to the γ-ray regimes for all sources, including multiwavelength spectral indices and redshifts. The full catalog is available online.

Results. We present the BlazEr1 catalog, containing 5865 sources, of which 2106 are associated with confirmed blazars. For 2966 sources, eROSITA provides the first X-ray data. The contamination from non-blazar sources of the entire sample is less than 11%. Most candidates exhibit properties typical for blazars. We present the properties of the entire X-ray detected blazar population, including the distributions of X-ray luminosities and photon indices, multiwavelength properties, and the blazar log N-log S distribution. Our catalog provides follow up targets, such as potential MeV and TeV blazars.

Conclusions. The BlazEr1 catalog provides a compilation of X-ray detected blazars and blazar candidates. The catalog serves as a starting point for exploiting further eROSITA surveys using the same methodology, enabling us to study the X-ray variability and a large number of spectral energy distributions of blazars in the future.