The SRG/eROSITA diffuse soft X-ray background
Astronomy and Astrophysics, vol. 714, pp. A85
Abstract
Context . The eROSITA bubbles (eRObub) were discovered in 2020 in the first SRG/eROSITA All-Sky Survey. They are some of the most extended structures in the X-ray sky. In projection, the eRObub encloses the γ -ray Fermi bubbles, and the northern eRObub appears to be bounded by the Loop I/North Polar Spur. Aims . Using eROSITA all-sky maps and spatially resolved spectra, we infer the three-dimensional structure and measure the hot gas properties of the eRObub. Methods . We fitted spectra binned to a constant signal-to-noise ratio and spectra with a high signal-to-noise ratio from custom regions to examine the gas properties in more detail. We fitted the morphology of eRObub using a parametrised geometrical model that describes a blast wave propagating from the Galactic Centre into an idealised Galactic halo. Results . The interior of the western eRObub is best characterised by two emission components with relatively uniform temperatures: a hotter component at kT = 0.60 ± 0.02keV, and a colder component at kT =0.21 −0.01 +0.03 keV, where the emission measure of the colder component is higher by about five times on average. Our spectra suggest sub-solar abundances (Z = 0.2 ± 0.1 Z ⊙ ), consistent with expectations for the Galactic halo. We found no conclusive evidence of α -element enhancement. In contrast, the abundances of the North Polar Spur are higher (Z > 0.5 Z ⊙ ). At face value, this disfavours a common origin. We spectrally confirmed an apparent cool shell at kT ~ 0.18−0.2keV surrounding the northern eRObub, assuming collisional ionisation equilibrium. We found no noticeable difference in X-ray emission in regions overlapping with the Fermi bubbles. Our geometrical model suggests that the horizontal size of the two eRObub is well constrained (semi-minor axis of ~6 kpc), but their vertical extent is uncertain because the observed X-ray emission is almost insensitive to the existence and location of a bubble cap. Additionally, a tilt (~30°) towards l ~ 220° is needed to reproduce the projected image of the northern eRObub, whereas the southern bubble requires a slight tilt.
Authors 18
-
Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Max-Planck-Institut für extraterrestrische Physik
-
Friedrich-Alexander-Universität Erlangen-Nürnberg
Affiliation as printed
Dr. Karl Remeis-Sternwarte and Erlangen Centre for Astroparticle Physics, Friedrich-Alexander Universität Erlangen-Nürnberg
-
Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Max-Planck-Institut für extraterrestrische Physik
-
Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Max-Planck-Institut für extraterrestrische Physik
-
University of Insubria · Brera Astronomical Observatory · Max Planck Institute for Extraterrestrial Physics · National Institute for Astrophysics
Affiliation as printed
Como Lake Centre for AstroPhysics (CLAP), DiSAT, Università dell’Insubria
INAF-Osservatorio Astronomico di Brera
Max-Planck-Institut für extraterrestrische Physik
-
Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Max-Planck-Institut für extraterrestrische Physik
-
Affiliation as printed
Department of Astronomy, Tsinghua University
-
Friedrich-Alexander-Universität Erlangen-Nürnberg
Affiliation as printed
Dr. Karl Remeis-Sternwarte and Erlangen Centre for Astroparticle Physics, Friedrich-Alexander Universität Erlangen-Nürnberg
-
Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Max-Planck-Institut für extraterrestrische Physik
-
Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Max-Planck-Institut für extraterrestrische Physik
-
Max Planck Institute for Extraterrestrial Physics · Max Planck Institute for Astrophysics
Affiliation as printed
Max-Planck-Institut für Astrophysik
Max-Planck-Institut für extraterrestrische Physik
-
Affiliation as printed
Department of Astronomy, Tsinghua University
-
Leiden University · Tokyo University of Science · RIKEN · Leiden Observatory · Space Research Organisation Netherlands
Affiliation as printed
Department of Physics, Tokyo University of Science
Leiden Observatory, Leiden University
RIKEN High Energy Astrophysics Laboratory
SRON Space Research Organisation Netherlands
-
Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Max-Planck-Institut für extraterrestrische Physik
-
Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Max-Planck-Institut für extraterrestrische Physik
-
University of Science and Technology of China
Affiliation as printed
Department of Astronomy, University of Science and Technology of China
School of Astronomy and Space Science, University of Science and Technology of China
-
Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Max-Planck-Institut für extraterrestrische Physik
-
Max Planck Institute for Extraterrestrial Physics
Affiliation as printed
Max-Planck-Institut für extraterrestrische Physik