Analysis of the spectral index trend in the filamentary regions of NGC 6086. Top: spectral index map of NGC 6086 at a resolution of 7 arcsec. Only pixels above 3σ for both LOFAR 144 MHz and uGMRT 675 MHz images are considered. Eighteen regions across the three filaments are selected in the map to investigate spectral index trends. The beam is shown in the bottom-left corner, and a reference scale is in the top-left one (the error map is presented in Fig. A.4). Centre and bottom: spectral index trends in the filaments colour-coded as shown in the legend. The central panel refers to , while the bottom panel refers to