Ratio of X-ray to UV luminosity for LFBOTs AT 2023fhn, AT 2018cow, and ZTF 20acigmel. The AT 2023fhn points use the dashed orange line in Fig. 6 and the two Chandra X-ray detections (errorbars reflect the X-ray uncertainties only). The black curve is the ratio of the Migliori et al. (2024) X-ray light-curve fit (see the solid black line, Fig. 7) and a broken power-law fit to the UV observations (the solid black line in Fig. 6). The small k-corrections are neglected in this comparison. The evolution past 200 days (drawn as a dashed line) is highly uncertain due to the sole X-ray detection. The ZTFacigmel data are from Ho et al. (2022), Bright et al. (2022), where we have taken the ratio of X-ray points and the power-law fit to the ZTFacigmel UV light curve in Fig. 6. The uncertainties on these points again solely reflect the X-ray measurement uncertainties.