Swift J0243.6+6124, the first Galactic ultra-luminous X-ray pulsar, was observed during its 2017-2018 outburst with AstroSat at both sub- and super-Eddington levels of accretion with X-ray luminosities of LX ∼ 7 × 1037 and 6 × 1038 ergs−1, respectively. Our broadband timing and spectral observations show that X-ray pulsations at ∼9.85s have been detected up to 150 keV when the source was accreting at the super-Eddington level. The pulse profiles are a strong function of both energy and source luminosity, showing a double-peaked profile with pulse fraction increasing from ∼ 10% at 1.65keV to 40–80 % at 70keV. The continuum X-ray spectra are well-modeled with a high energy cut-off power law (Γ ∼ 0.6-0.7) and one or two blackbody components with temperatures of ∼ 0.35 keV and 1.2keV, depending on the accretion level. No iron line emission is observed at sub-Eddington level, while a broad emission feature at around 6.9 keV is observed at the super-Eddington level, along with a blackbody radius (121−142km) that indicates the presence of optically thick outflows.
- X-rays: binaries
- Pulsars: individual (Swift J0243.6+6124)