Spectral index maps of the Toothbrush, at resolution, showing remarkably similar spectral index patterns up to 6 GHz. The variations in the spectral index at the outer edge along the relic are clearly visible, reflecting inhomogeneities in the injection index. Top: low-frequency spectral index maps between 150 and 1500 MHz. Bottom: high-frequency spectral index maps between 1.5 and 6 GHz. The color bar shows spectral index α from −2.5 to 0.5. Bottom: all maps, contour levels are drawn at [1, 2, 4, 8, …]×4σ_rms and are from the 150 MHz LOFAR image. These maps were created using the IM2, IM6, IM11, IM15, and IM19 (see Table 2 for image properties).