Modelling the optical/UV emission of Swift J0243.6+6124 during its 2017–2018 giant outburst

The Be X-ray binary Swift J0243.6+6124 underwent a super-Eddington giant outburst that lasted from September 2017 to February 2018. The reached luminosity was so high, that it became the first Ultraluminous X-ray pulsar (ULXP) in the Galaxy. Simultaneously to this X-ray outburst, optical and UV outbursts were observed. In this work, we try to explain the origin of this emission. We built a physical modelling considering the heating of the surface of the Be star, the emission from the viscously heated accretion disk, and the irradiation of this accretion disk by the central X-ray source. Using this model, we fit the Spectral Energy Distributions built with the available photometric measurements obtained each day along the outburst.