Seeing to the Event Horizon: Probing Accretion Physics with X-ray Reflection
Abstract
Accretion onto supermassive black holes in active galactic nuclei is known to power some of the most luminous objects we see in the Universe, which through their vast energy outputs must have played an important role in shaping the large scale structure of the Universe we see today. Much remains unknown, however, about the fine details of this process; exactly how energy is liberated from accretion flows onto black holes, how the 'corona' that produces the intense X-ray continuum is formed and what governs this process over time. I will outline how the detection of X-rays reflected from the discs of accreting material around black holes by the present generation of large X-ray observatories, shifted in energy and blurred by relativistic effects in the strong gravitational field close to the black hole, has enabled measurements of the inner regions of the accretion flow in unprecedented detail. In particular, exploiting the shift in energy of atomic emission lines by relativistic effects as a function of location on the disc has enabled the measurement of the illumination pattern of the accretion flow by the X-ray continuum from which the geometry of the emitting region can be inferred and how the detection of time lags between the primary and reflected X-rays owing to the additional path the reflected rays must travel between the corona and the disc places further constraints on the nature of the emitting corona. These techniques allow the evolution of the corona that accompanies transitions from high to low X-ray flux to be studied, giving clues to the physical process that forms and powers the intense X-ray source and uncovering evidence for the potential launching of jets. I will discuss the great steps forward in understanding accretion physics that can be made with the Athena X-ray observatory, combining detailed analysis of observations with predictions and models from general relativistic ray tracing simulations. In particular, I will discuss how high resolution X-ray spectra can probe the geometry and physics of both the X-ray emitting corona and the accretion disc itself and how this next generation observatory will enable detailed energyresolved measurements of X-ray reverberation which will produce not just a static picture but a dynamic one of the processes by which energy is injected into and propagates through the corona and accretion flow to power some of the most luminous objects we see in the Universe.
- Publication:
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Exploring the Hot and Energetic Universe: The first scientific conference dedicated to the Athena X-ray observatory
- Pub Date:
- September 2015
- Bibcode:
- 2015eheu.conf...76W