Figure shows three frequency spectral index map and its uncertainties. Upper panel: spectral index map made using LOFAR 144 MHz, GMRT 323 MHz, and GMRT 612 MHz maps (described in Sect. 3.5). The GMRT 323 MHz contours are overplotted in black with six levels spaced in log scale with the lowest level of 3σ (Table 3). The red circle indicates the location of the radio core or host galaxy. In the bottom left corner, the red dot represents the beam of 13″ × 13″. Lower panel: spectral index error map.