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A long stare at Hercules X-1: investigating the vertical structure of an accretion disc wind

Presentation #110.01 in the session “Stellar/Compact (Poster)”.

Published onApr 01, 2022
A long stare at Hercules X-1: investigating the vertical structure of an accretion disc wind

Hercules X-1 is a famous neutron star X-ray binary exhibiting a warped, precessing accretion disc. The disc is observed almost edge-on, offering us the unique opportunity to study an accretion flow at changing sightlines to the central source. We previously detected a strongly variable disc wind in Her X-1 using archival datasets. We proposed that the observations are sampling varying sightlines towards the neutron star and are thus measuring the wind properties at different locations and heights above the disc. In this talk, I will present new results on a recent Large XMM-Newton campaign (380 ks) from August 2020 that sampled a significant fraction of a single precession cycle. This, combined with Chandra snapshots, results in one of the longest high-resolution X-ray datasets ever taken on an X-ray binary. We show that the optical depth of the ionized wind strongly anti-correlates with the precession phase, and thanks to the high quality observations and detailed photoionization modelling, we determine that this evolution is due to a decrease in wind column density as the precession cycle progresses. This indicates either that the wind is much weaker at large heights above the disc (sampled at later precession cycle phases), or that we are observing it at much larger distances from the X-ray source. I will present these new results on precision tomography of an accretion disc wind and other new results from this extremely rich dataset.


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