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We report the discovery of the bright reflected emission component in thesuper-Eddington state of the ULX pulsar Swift J0243.6+6124, based on the NuSTARobservations of the source during its 2017 outburst. The flux of the reflectedemission is weakly variable over the pulsar phase while the direct emissionshows significantly larger pulsation amplitude. We propose that in this systemthe neutron star finds itself in the centre of the well formed by the inneredge of the geometrically thick super-Eddington accretion disc truncated by themagnetic field of the pulsar. The aspect ratio of the well is H/R \sim 1. Theinner edge of the truncated disc is continuously illuminated by the emission ofthe accretion column giving rise to the weakly variable reflected emission. Asthe neutron star rotates, its emission sweeps through the line of sight, givingrise to the pulsating direct emission. From Doppler broadening of the ironline, we measure the truncation radius of the accretion disc \sim 50 R_g. Theinferred dipole component of the magnetic field is consistent with previousestimates favouring a not very strong field. The uniqueness of this system isdetermined by its moderately super-Eddington accretion rate and the moderatemagnetic field so that the inner edge of the truncated geometrically thickaccretion disc is seen from the neutron star at a large solid angle.

ULX pulsar Swift J0243.6+6124 observations with NuSTAR -- dominance of reflected emission in the super-Eddington state