Swift/XRT and optical light curves (MASTER CR band, X-shooter, GROND r′). Note that the optical data of the transient were obtained via image subtraction after 0.2 days, and therefore the contribution of the host is also subtracted. We highlight in cyan the epochs used in the optical-to-XRT SED fitting. Vertical lines highlight epochs with spectroscopic coverage. The dotted lines are the best fit of the optical light curve obtained in Section 4.2, which we have also normalised to the X-rays for data after 5 ks, i.e., excluding the first Swift orbit, which clearly shows that these early data are offset from the fit (see Sect. 4.3).