The SRG/eROSITA all-sky survey: First X-ray catalogues and data release of the western Galactic hemisphere (2401.17274v1)

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 930000 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 show that the number counts of X-ray sources in eRASS1 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_{0.5-2 keV} > 5 \times 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.

• The paper presents the first comprehensive X-ray catalogue from the SRG/eROSITA survey, listing nearly 930,000 sources in the western Galactic hemisphere.
• It employs a continuous scanning mode with high astrometric precision to ensure uniform exposure and reliable source positioning.
• The survey advances X-ray astronomy by resolving a significant fraction of the cosmic X-ray background and identifying diverse astronomical phenomena.

Overview of the SRG/eROSITA All-Sky Survey

The document presents the results and methodologies of the SRG/eROSITA all-sky survey, focusing on the first data release that covers the western Galactic hemisphere. This extensive survey leverages the eROSITA instrument on board the Russian-German Spektr-RG (SRG) mission, designed to map the X-ray sky with unprecedented depth and breadth.

Key Findings

• Source Catalogues: The survey has generated a comprehensive catalogue of nearly 930,000 X-ray sources in the energy range of 0.2-2.3 keV. This represents a significant increase of over 60% in the number of known X-ray sources compared to previously published catalogues.
• Energy Band Detection: Alongside the main catalogue, a secondary catalogue lists 5,466 sources detected in a harder energy range of 2.3-5 keV. This marks the first true imaging survey of the sky above 2 keV, highlighting the capacity of eROSITA to explore high-energy phenomena.
• Wide-Ranging Source Types: The catalogues encompass a wide array of astronomical objects, from point-like to extended X-ray sources, depicting a variety of galactic and extra-galactic phenomena. This includes isolated neutron stars, binary systems, supermassive black holes, and more.
• Observational Strategy: The data were collected through a continuous scanning mode, achieving uniform exposure over the sky. This strategy addresses observational consistency and ensures homogeneous data quality across the survey.

Technical Achievements

• Astrometric Precision: Measurements of astrometric accuracy were validated through cross-comparison with established X-ray and multi-wavelength catalogues. This ensures the reliability of source positioning and classification within the catalogues.
• Flux Completeness: The survey confidently resolves approximately 20% of the cosmic X-ray background in the 1-2 keV range into discrete sources.
• Sensitivity and Exposure: Exposure maps indicate varying depths of survey coverage with more than 10,000 seconds of cumulative exposure near the ecliptic poles, while median detections reach a flux limit of $5 \times 10^{-14}$ erg s$^{-1}$ cm$^{-2}$ at 50% completeness.

Implications

The eROSITA all-sky survey not only enhances the existing inventory of X-ray sources but also serves as a crucial dataset for studying the structure and evolution of the universe. With its unmatched combination of area coverage and depth, eROSITA provides a new window into X-ray astronomy, promising to deepen our understanding of fundamental astrophysical processes across different scales.

Future Prospects

The survey opens up pathways for further exploration of cosmic phenomena, particularly those relating to dark matter and energy, galaxy evolution, and the physics of high-energy astrophysical systems. Subsequent data releases and continued observations are expected to refine the current catalogues and expand upon the survey’s scientific contributions.

Overall, the SRG/eROSITA survey stands as a significant milestone in X-ray astrophysics, delivering comprehensive and detailed insights into the X-ray universe, laying groundwork for future astronomical discoveries and theoretical advancements.