Evolution of Hα emission flux for AT 2019abn. Black circles show SPRAT measurements, with grey triangles showing OSIRIS measurements. The uncertainties on the calibration and measurements themselves will generally be relatively low. In some cases there may be significant uncertainties from the sky subtraction however, due to the complicated M51 background. The u′-band (purple), B-band (blue) and r-band (orange) optical light curves are also shown for reference (in relative flux, rather than magnitude, and not to any absolute scale).