Panel a: light curve from Swift/UVOT, with one data point per observation. Black circles are u-filter, red squares are uvw1-filter, green triangles are uvw2-filter, and blue diamonds are uvm2-filter. Panel b: Swift/XRT light curve in the 0.3–10 keV energy band, with the same binning as the UVOT light curve. Dotted lines mark the times of maximum light in the UVOT data, assuming a constant period of P_opt = 63:9 d and dashed lines mark the maximum of the folded XRT profile with a constant period of P_X = 66:9 d.