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X-ray emission and absorption features during an energetic thermonuclear X-ray burst from IGR J17062-6143

Type-I X-ray bursts are thermonuclear explosions occurring in the surface layers of accreting neutron stars. These events are powerful probes of the physics of neutron stars and their surrounding accretion flow. We analyze a very energetic type-I X-ray burst from the neutron star low-mass X-ray binary IGR J17062-6143 that was detected with Swift on 2012 June 25. The light curve of the ~18 min long X-ray burst tail shows an episode of ~10 min during which the intensity is strongly fluctuating by a factor of ~3 above and below the underlying decay trend, on a time scale of seconds. The X-ray spectrum reveals a highly significant emission line around ~1 keV, which can be interpreted as a Fe-L shell line caused by irradiation of cold gas. We also detect significant absorption lines and edges in the Fe-K band, which are strongly suggestive of the presence of hot, highly ionized gas along the line of sight. None of these features are present in the persistent X-ray spectrum of the source. The time scale of the strong intensity variations, the velocity width of the Fe-L emission line (assuming Keplerian motion), and photoionization modeling of the Fe-K absorption features each independently point to gas at a radius of ~1E3 km as the source of these features. The unusual X-ray light curve and spectral properties could have plausibly been caused by a disruption of the accretion disk due to the super-Eddington fluxes reached during the X-ray burst.