Unit:
Department of PhysicsLibrary of the School of Science
Author:
AKALESTOS KONSTANTINOS - RAFAIL
Supervisors info:
Δρ. Αντώνης Γεωργακάκης, Διευθυντής Ερευνών, ΙΑΑΔΕΤ, Εθνικό Αστεροσκοπείο Αθηνών
Μαρία Πετροπούλου, Επίκουρη Καθηγήτρια, Τμήμα Φυσικής, ΕΚΠΑ
Original Title:
Probing scaling Relations of AGN accretion parameters through the ensemble QSO X-ray variability in XMM- Newton light Curves
Translated title:
Probing scaling Relations of AGN accretion parameters through the ensemble QSO X-ray variability in XMM- Newton light Curves
Summary:
Active Galactic Nuclei exhibit characteristic stochastic flux fluctuations in their Xray emission, providing important insights into the accretion physics around supermassive black holes. Despite this, few systematic studies have targeted variability in AGNs with high Eddington ratios and massive black holes, particularly on shorter timescales that closely reflect conditions near the central engine. In this thesis, we study intrinsic X-ray variability through normalized excess variance (NXSV) using a sample of optically-selected SDSS QSOs also found in observations from XMM-Newton’s Serendipitous Source Catalog. Our sample spans Eddington ratios λEdd ≈ 10−2 to the Eddington limit and black hole masses MBH ≈ 108–1010M⊙. Weemployacustomprocessingpipelineforoptimallightcurveextractionandutilize a newBayesianhierarchical methodology fit for the Poisson nature of the light curves to estimate mean NXSV across populations of physically similar QSOs. Our analysis reveals a positive correlation between NXSV and λEdd, challenging earlier studies reporting an anti-correlation. This increased short-term X-ray variability at λEdd may result from changes in the corona’s geometry or from enhanced turbulence associated with transitions to slim-disk accretion. Conversely, variability shows no clear scaling with MBH, although comparisons with theoretical models suggest a subtle correlation could be obscured by the uncertainties inherent to our values.
Main subject category:
Science
Keywords:
Active Galactic Nuclei, X-ray Observations, Observational Astronomy, Normalized Excess Variance, Accretion Physics, AGN Variability
