Low-frequency radio spectral index of the central compact source. Blue points show flux measurements from the literature (Table 3), and red points show, in order of frequency, the new VLITE, GMRT, VLA, and ALMA measurements presented here. Flux measurements (excluding the 92 GHz measurement from ALMA) were fitted with a singular power law spectrum, shown in black (α = −1.02). We note that the uncertainties are too small to be seen on the scale of the plot.