NuSTAR Spectroscopy of MAXI J1820+070: Testing Black Hole Coronal Contraction
Abstract
During black hole outbursts, the geometry of its accretion flow can change over time. In quiescence, the black hole initially emits high-energy (hard) x-rays dominated by the hot corona, then translates into the soft spectrum that is strongly influenced by the accretion disk. Although it was widely believed that this progression was caused by the advection-dominated accretion flow (ADAF) where the disk moves in towards the event horizon, Kara et al. (2019) suggest a new paradigm through timing analysis of MAXI J1820+070; instead of the radius of the inner edge of the accretion disk maximally extending to 1 RISCO, it is a result of reduction in the spatial extent of the corona. By using a general relativistic code that uses spectroscopy rather than timing constructed parameters, the coronal contraction theory was tested. After thorough spectral analysis of the NuSTAR observation of MAXI J1820+070 from March and June observations, the results contradicted the results presented in Kara et al. The black hole transient MAXI J1820+070 does transition from a hard (power-law index around 1.5) state to a softer (power-law index around 1.6) state, but it occurs through the movement of the inner edge of the disk and not by the transformed geometry of the corona.
- Publication:
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American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23537902R