Top panel: spectral index map between 45 and 145 MHz at a spatial resolution of 13″ × 13″ (left), 23″ × 23″ (middle) and 37″ × 37″ (right). Bottom panel: relative spectral index error $\mathrm{\Delta }{\alpha }_{145\mathrm{MHz}}^{45\mathrm{MHz}}$. Pixels with surface brightness values below 2σ_rms in the two images were blanked and $[3,6,12,24,48,96]\times {\sigma }_{\mathrm{rms}}^{45\mathrm{MHz}}$ contours are over-plotted.