the host galaxy (section \[sec:host\]), and scaling the predicted flux by a factor 0.2, i.e. the fraction of the host light within a $5''$ aperture in the PanSTARRS $g$-band image of the galaxy. We checked that this provides a reliable estimate of the host flux by re-extracting the UVOT light curve using a $30''$ aperture to fully capture both the transient and host flux, and subtracting the model host magnitudes with no scaling.

Comparing the $5''$ light curves to the $30''$ light curves, we find a good match in the $U$ and $UVW1$ bands (but with much better S/N ratio in the $5''$ case). In the bluer $UVM2$ and $UVW2$ bands, where the host SED and light profile is less constrained, we find that scaling the host flux by a factor 0.1 before subtraction yields better agreement, and we adopt this as our final light curve. In all cases, we propagate the uncertainty in the host contribution, determined using the standard deviation of samples drawn from the SED fit. The complete, host-subtracted UV and optical light curves from *Swift*, LCO, ZTF and ATLAS are shown in Figure \[fig:phot\].

*Swift* XRT data
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We processed the XRT data using the online 