Accurate distances of the Galactic spiral arms from dust-scattered X-ray emission of gamma-ray bursts
Year: 2026
Type: article
Abstract: The details of the spiral structure of the Milky Way are still debated due to the large uncertainties in the distance estimates obtained through the most common tracers. However, X-ray dust scattering rings produced by short extragalactic X-ray transients provide a direct method to measure the 3D distribution of interstellar clouds up to the edges of our Galaxy with a precision of a few percent. We report on an analysis of all the available XMM-Newton and Chandra follow-up observations of three low-latitude gamma-ray bursts: GRB 031203 (l ≃ 255°, b ≃ −5°), GRB 160623A (l ≃ 84°, b ≃ −3°), and GRB 221009A (l ≃ 53°, b ≃ 4°). The previous detection of X-ray rings in these observations, produced by dust clouds located beyond 5 kpc, can be associated with dust in the Perseus, Outer, and Outer Scutum-Centaurus arms, thus providing direct distance measurements to these structures along three distinct lines of sight. We identify two additional rings in the direction of GRB 160623A produced by dusty clouds at 6.91 ± 0.06 kpc and 9.9 ± 0.6 kpc, and we confirm – through a second XMM-Newton observation – the presence of one cloud at 9.7 ± 0.4 kpc toward GRB 031203. We also accurately measured the distance of dusty clouds up to 19.0 ± 0.2 kpc based on the analysis of one Chandra and four XMM-Newton observations of GRB 221009A. The small statistical and systematic uncertainties of these measurements place tight constraints on the geometry of the outer Milky Way and reveal significant deviations from current models, which critically depend on spectroscopy-based Galactic rotation curves at large distances.
Institutions: Istituto Universitario di Studi Superiori di Pavia, Istituto di Astrofisica Spaziale e Fisica Cosmica di Milano, National Institute for Astrophysics, Centre National de la Recherche Scientifique, Université Paris Cité, Université Paris Sciences et Lettres, Arcetri Astrophysical Observatory, École Normale Supérieure - PSL, Sorbonne Université, Laboratoire de Physique de l'Ecole Normale Supérieure, Ruđer Bošković Institute, University of Zagreb, Faculty of Electrical Engineering and Computing in Zagreb, Istituto di Astrofisica Spaziale e Fisica cosmica di Palermo
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funder: European Commission
OpenAlex ID: W7160859291
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