Spectral index maps for SNR G46.8–0.3 constructed between (a) 200 MHz and 1.4 GHz and (b) 1.4 and 4.8 GHz. The images used are from GLEAM, THOR+VGPS, and GB6 surveys (see Sect. 2.1). Regions with flux densities lower than 4σ level of the respective rms noise in each image were clipped. The colour scale displayed to the right indicates the spectral index measured (with a 4′ resolution) over the SNR at both frequency bands. Dark and light green contours represent the intensity of the FUGIN ¹²CO (J = 1–0) molecular line emission (at a 2′ spatial resolution) integrated in the 30–50 km s⁻¹ (levels: 500 and 800 K km s⁻¹) and 50–66 km s⁻¹ (levels: 1100 and 1400 K km s⁻¹) ranges, respectively. A detailed treatment of the molecular features associated with G46.8–0.3 is presented in Sect. 5.