QPO modulation of the short-term time-lags in MAXI J1820+070
Abstract
X-rays from black hole X-ray binaries (BHXRBs) are emitted from different regions in the accretion flow, mainly the disk and the corona. Variability in these different components is correlated and exhibits time-lags. Short time-scale (∼0.1 s) broadband noise variability shows time-lags which are thought to be due to X-ray reverberation and therefore should be linked to disk-corona geometry. The corona is also associated with quasi-periodic oscillations (QPOs), which are variations in flux on a time-scale of a few seconds. They are thought to arise due to geometric variations in the corona, e.g. caused by precession of an inner, hot accretion flow. Connecting short-term time-lags and QPOs can shed new light on the mechanism behind QPOs, as changes in coronal geometry will also influence the reverberation lags. The extensive observations by NICER of bright BHXRB MAXI J1820+070 have led to a spectral-timing data set of unprecedented quality, which enables testing new methods to explore the connection between short-term time-lags and QPOs. I will show how Fourier filtering techniques can be used to reveal how short-term time-lags vary with QPO phase and on other time-scales. I find that, in MAXI J1820+070, there exists a linear relation between the short-term lags and the coronal flux across a range of time-scales. However, the QPO frequency corresponds to the time-scale with the strongest fluctuations in short-term time-lags, consistent with both QPO and lags being linked to changes in coronal geometry.
- Publication:
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44th COSPAR Scientific Assembly. Held 16-24 July
- Pub Date:
- July 2022
- Bibcode:
- 2022cosp...44.2346B