Spectral index and spectral index maps of A1550 between different frequencies. Top left: spectral index map between 54 MHz and 144 MHz, generated by combining total intensity maps produced with matching uv-cut 80λ − 14kλ. Contours are at 3σ from the LBA map. The beam is 25″ ×13″. Top middle: spectral index map between 144 MHz and 400 MHz, generated by combining total intensity maps produced with matching uv-cut 80λ − 14kλ. The beam is 20″ × 17″. Top right: spectral index map between 400 MHz and 1.4 GHz, generated by combining total intensity maps produced with matching uv-cut 140λ − 14kλ. The beam is 38″ × 32″. Bottom left: spectral index error map between 54 MHz and 144 GHz. Bottom middle: spectral index error map between 144 MHz and 300 MHz. Bottom right: spectral index error map between 400 MHz and 1.4 GHz.