Aperiodic variability and lags: disentangling the disk and corona
Abstract
Starting with XMM-Newton and turbo-charged by NICER, spectral-timing studies of black hole X-ray binaries are shedding new light on the disk-corona connection and inner region geometry in accreting black holes. In my talk I will focus on the observations and interpretation of lags in the aperiodic variability, between the disk and coronal power-law emission, as well as between different energies in the power-law emission. I will describe some of the challenges with explaining both the disk and power-law behaviour together. I will then show how the complex frequency and energy-dependent behaviour can be interpreted in terms of the different ways that the disk and corona communicate signals to one another: propagating mass accretion fluctuations, seed photon variations and X-ray reverberation. The combination of these effects leads naturally to lags which are sensitive to different aspects of the coronal geometry. Moreover, models incorporating all of these processes can naturally explain the switch from hard to soft lags at high frequencies. The soft lags are due primarily to seed photons and propagation fluctuations leading the disk reverberation signal, rather than the reverberation light travel time itself. This suggests that coronae are more compact than has been inferred based on recent lag studies.
- Publication:
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44th COSPAR Scientific Assembly. Held 16-24 July
- Pub Date:
- July 2022
- Bibcode:
- 2022cosp...44.1748U