SwiftJ0243.6+6124, the first Galactic ultra-luminous X-ray pulsar, was observed during its 2017-2018 outburst with \emph{ AstroSat} at both sub- and super-Eddington levels of accretionwith X-ray luminosities of $L_{ X}{ \sim}7{ \times}10^{ 37}$ and $6{ \times}10^{ 38}$$ergs^{ -1}$, respectively.Our broadband timing and spectral observations show that X-ray pulsations at ${ \sim}9.85\rm{ s}$ have been detected up to 150keV when the source was accreting at the super-Eddington level.The pulse profiles are a strong function of both energy and source luminosity,showing a double-peaked profile with pulse fraction increasing from $\sim$$10{ \%}$ at $1.65\rm{ keV}$ to 40--80$\%$ at $70\rm{ keV}$.The continuum X-ray spectra are well-modeled with a high energy cut-off power law($\Gamma$${ \sim}$0.6-0.7) and one or two blackbody components with temperatures of $\sim$0.35$\rm{ keV}$ and $1.2\rm{ keV}$, depending on the accretion level.No iron line emission is observed at sub-Eddington level, while a broad emission feature at around 6.9keV is observed at the super-Eddington level, along with a blackbody radius($121-142\rm{ km}$) that indicates the presence of optically thick outflows.
Categories: astro-ph.HE