Optical light curve and Icarus model for the companion star of PSR J0610−2100. Vertical lines show the measured magnitudes and their 1σ uncertainties. Where the counterpart is not detected in an image, we plot 2σ upper limits instead, denoted by downward-pointing arrows. Dashed curves show the flux in each band as predicted by our best-fitting Icarus model, solid curves show the same model after allowing for small (0.1 mag) offsets between the photometric calibration and the model normalisation. An orbital phase of ϕ = 0 corresponds to the pulsar’s ascending node; the companion star’s superior conjunction is at phase ϕ = 0.75.