LAUSR

We acknowledge the efforts of the Swift planners. Swift and NuSTAR Data were retrieved from the Swift and NuSTAR archive at HEASARC/GSFC, and from the UK Swift Science Data Centre. We also used the CFHT archive hosted at the Canadian Astronomy Data Centre operated by the National Research Council of Canada with the support of the Canadian Space Agency, and the WFCAM UKIRT data from the UKIDSSDR10PLUS data release from the WFCAM archive at the Royal Observatory Edinburgh. This work has been supported by the UK Space Agency under grant ST/P002323/1 and the UK Science and Technology Facilities Council under grant ST/N00811/1. QH is supported by a UCL MSSL Summer Research Studentship. SRO gratefully acknowledges the support of the Leverhulme Trust Early Career Fellowship. SC acknowledges the support of under ASI-INAF contract I/004/11/1.