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The Densities of Black Hole Accretion Discs and Their Implications in X-ray Data

Presentation #100.13 in the session AGN.

Published onJul 01, 2023
The Densities of Black Hole Accretion Discs and Their Implications in X-ray Data

Conventionally, the standard thin disc model by Shakura and Sunyaev is utilised to explain the optical and UV observations of AGN, where the thermal emission from the accretion disc in AGN dominates. But observations suggest dramatic energy exchanges between the disc and the corona: most of the accretion power, e.g. up to 90%, must be dissipated in the hot corona to explain the multi-wavelength data of AGN. One of the consequences of having a high coronal illumination is an even higher density in a high-accretion rate, radiation-dominated disc compared to the predictions of the standard thin disc model.

I will present the X-ray spectral modelling of AGN by considering a variable density parameter for the surface of the innermost accretion discs, and the effects of a high density parameter on the resulting reflected emission. This key attribute has been long overlooked by previous work where a low, fixed density was assumed but promises to reveal key insights into the detailed disc structures, disc energy exchanges and the connection between supermassive and stellar-mass black holes. Moreover, the disc model with a high-density parameter provides a solution to previously commonly seen super-solar iron abundance problems in data analyses and an explanation for the puzzling soft excess emission in AGN. In the end, I will summarise the latest progress in high-density disc reflection spectroscopy and demonstrate our plan for the development of relevant spectral models.

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