Spectral index of the GReET tail in A1033 tail as a function of distance from the host, from Fig. 3 in de Gasperin et al. (2017). The red points show the expected steepening of an α₀ = −0.65 spectrum with a low velocity for the radiating plasma, while the very modest amount of steepening in the final portion of the tail is consistent with a much higher transport velocity of 15 000 km/s, as shown in blue. The bottom plot, in solid black, shows the inferred direction of the host’s motion at each position in the tail, assuming the tail is left behind material. The variation in direction around 400 kpc is assumed to arise from a transverse flow, not from a change in the host velocity.