Published in

Oxford University Press (OUP), Monthly Notices of the Royal Astronomical Society: Letters, 2019

DOI: 10.1093/mnrasl/slz120

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Hot, dense HeII outflows during the 2017 outburst of the X-ray transient Swift J1357.2-0933

This paper was not found in any repository, but could be made available legally by the author.
This paper was not found in any repository, but could be made available legally by the author.

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Data provided by SHERPA/RoMEO

Abstract

Abstract Time-resolved SALT spectra of the short-period, dipping X-ray transient, Swift J1357.2-0933, during its 2017 outburst has revealed broad Balmer and HeII λ4686 absorption features, blue-shifted by ∼600 km s−1. Remarkably these features are also variable on the ∼500s dipping period, indicating their likely association with structure in the inner accretion disc. We interpret this as arising in a dense, hot (≳ 30, 000K) outflowing wind seen at very high inclination, and draw comparisons with other accretion disc corona sources. We argue against previous distance estimates of 1.5kpc and favour a value ≳ 6kpc, implying an X-ray luminosity LX ≳ 4 × 1036 erg s−1. Hence it is not a very faint X-ray transient. Our preliminary 1D Monte-Carlo radiative transfer and photoionization calculations support this interpretation, as they imply a high intrinsic LX, a column density NH ≳ 1024cm−2 and a low covering factor for the wind. Our study shows that Swift J1357.2-0933 is truly remarkable amongst the cohort of luminous, galactic X-ray binaries, showing the first example of HeII λ4686 absorption, the first (and only) variable dip period and is possibly the first black hole ‘accretion disc corona’ candidate.

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