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Published September 11, 2016 | Submitted
Journal Article Open

A quasi-periodic modulation of the iron line centroid energy in the black hole binary H 1743-322

Abstract

Accreting stellar-mass black holes often show a 'Type-C' quasi-periodic oscillation (QPO) in their X-ray flux and an iron emission line in their X-ray spectrum. The iron line is generated through continuum photons reflecting off the accretion disc, and its shape is distorted by relativistic motion of the orbiting plasma and the gravitational pull of the black hole. The physical origin of the QPO has long been debated, but is often attributed to Lense–Thirring precession, a General Relativistic effect causing the inner flow to precess as the spinning black hole twists up the surrounding space–time. This predicts a characteristic rocking of the iron line between red- and blueshift as the receding and approaching sides of the disc are respectively illuminated. Here we report on XMM–Newton and NuSTAR observations of the black hole binary H1743−322 in which the line energy varies systematically over the ∼4 s QPO cycle (3.70σ significance), as predicted. This provides strong evidence that the QPO is produced by Lense–Thirring precession, constituting the first detection of this effect in the strong gravitation regime. There are however elements of our results harder to explain, with one section of data behaving differently than all the others. Our result enables the future application of tomographic techniques to map the inner regions of black hole accretion discs.

Additional Information

© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2016 May 19. Received 2016 May 19; in original form 2016 April 15. Published: 25 May 2016. AI acknowledges support from the Netherlands Organisation for Scientific Research (NWO) Veni Fellowship, grant number 639.041.437. He thanks Martin Heemskerk for assistance making the plots in this paper. He also acknowledges useful conversations with Dom Walton, Matteo Bachetti and Brian Grefenstette about NuSTAR data reduction, and useful conversations with Andrew King about disc warping. MJM appreciates support via an STFC Ernest Rutherford Fellowship. CD acknowledges support from the STFC consolidated grant ST/L00075X/1. DA acknowledges support from the Royal Society. MA is an International Research Fellow of the Japan Society for the Promotion of Science. We thank the anonymous referee for constructive comments.

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