Speaker
Description
Geometric constraints on inner regions of active galactic nuclei (AGN) are crucial for uncovering the behaviour of matter in extreme gravitational environments and thus for providing tests of general relativity. A time lag between different energy bands occurs due to the different path lengths for photons which have travelled directly to us after being Compton up-scattered in the corona, and for those reflected by the surrounding accretion disc. The lag-energy spectrum therefore holds information on the geometry of the system and has been fit to provide constraints on geometric parameters. This technique is impacted by instrumental noise and stochastic variability, which is intrinsic to the accretion process and decreases the coherence between light curves. A reduced coherence results in larger uncertainties between the lag and therefore geometry. Quasi-periodic oscillations (QPOs) are extremely coherent, producing a peak in coherence observed at a certain frequency, and reduces the effects of the intrinsic stochastic variability on geometric uncertainties. In this work, we investigate the lags produced at the QPO frequency versus the entire broadband frequency range, showing that the increased coherence of this signal can be leveraged to provide better constraints in geometric properties surrounding AGN.