Understanding the structure of the accretion flow in black hole binaries from the energy-dependent variability
Abstract
The nature and geometry of the accretion flow of black hole X-ray binaries in the low/hard state are still controversial as results from spectral fitting are not unique. We use the independent information carried by the fast variability (milliseconds to seconds) to break these degeneracies. Many properties of this variability can be interpreted qualitatively in a propagating fluctuations scenario, where mass accretion rate fluctuations generated by turbulence propagate down through a hot inner flow. However, it has proved difficult to make a quantitative model that can fully describe the variability across the entire energy band, especially one that simultaneously fits the spectral data. We have developed a new spectral-timing model, and applied it to the brightest black hole binary, MAXI J1820+070, observed by NICER and Insight HXMT from 0.5 keV up to 200 keV. We show how our model captures the essence of the fast variability properties, how they change with energy, and how it gives new insight into the structure of the accretion flow close to the black hole.
- Publication:
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44th COSPAR Scientific Assembly. Held 16-24 July
- Pub Date:
- July 2022
- Bibcode:
- 2022cosp...44.2351K