CRA Seminar: Ethan Partington, IA-FORTH (Host Laura Cadonati)

Title: Probing the inner geometry of AGN accretion flows and searching for SMBHB candidates in large optical sky surveys

Abstract: Observations of the AGN Fairall 9 with NICER and Swift revealed a strong relationship between the flux of the UV continuum and the X-ray soft excess, indicating the presence of a “warm” Comptonized region which may act as a second reprocessor between the “hot” X-ray corona and the accretion disk. This has previously been suggested as an explanation for the weak X-ray/UV correlation observed in many AGN, and it can be confirmed using NICER’s unprecedented spectral coverage of X-ray variability on timescales of days to years. Our separate NICER reverberation mapping campaign on the AGN NGC 7469 provides no evidence for a warm corona, suggesting that there is no uniform prescription for the geometry of the inner accretion flow across all AGN. In this seminar, I will present the X-ray spectral modeling results from both AGNs in the context of understanding their geometries and energetic properties. I will also discuss the Null-Signal Template (NST) method, a new data-driven approach to testing the significance of possible periodic signals in quasar light curves. NST employs Bayesian statistics to differentiate between supermassive black hole binary (SMBHB) signals and the complex noise of individual quasars. I will share new tests on the validity of the NST method using simulated LSST-like light curves and discuss the prospects for the application of NST to SMBHB detection in both existing and upcoming quasar surveys.