LoS geometry of M53A relative to Galactic bubble structures. Top: composite all-sky map (modified from P. Predehl et al. 2020) showing the Fermi bubbles (dark red, γ-ray) and eROSITA bubbles (cyan, 0.6–1.0 keV X-ray). The yellow star marks M53A. Bottom: 3D geometric model of the M53A LoS relative to the modeled bubble structures, with dimensions based on the thick-shell model of P. Predehl et al. (2020).