AstroSat Observations of the first Galactic ULX Pulsar Swift J0243.6+6124

Aru Beri, Sachindra Naik, K. P. Singh, Gaurava Kumar Jaisawal, Sudip Bhattacharyya, Philip Charles, Wynn C G Ho, Chandreyee Maitra, Dipankar Bhattacharya, Gulab C Dewangan, Matthew Middleton, Diego Altamirano, Poshak Gandhi, Harsha Raichur

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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.
Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Pages (from-to)565–575
Publication statusPublished - 2020


  • X-rays: binaries
  • Pulsars: individual (Swift J0243.6+6124)

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