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Access Type
WSU Access
Date of Award
January 2024
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Physics and Astronomy
First Advisor
Edward Cackett
Abstract
The AGNs Fairall 9 and Mrk 817 were targeted by NICER, Swift, and other space- and ground-based observatories for the two longest (>1000~day) coordinated multiwavelength AGN monitoring campaigns to date. The following analysis of NICER spectra taken at a two day cadence provides new insights into the structure and heating mechanisms of central black hole environments. At the start of the AGN STORM~2 campaign on Mrk~817 in 2020, NICER, HST, and XMM-Newton revealed the presence of a new partially-covering ionized obscurer, consistent with a clumpy disk wind launched from the inner broad line region. Observations of 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, but could only be confirmed by NICER due to its unprecedented spectral coverage of X-ray variability on timescales of days to years. My separate NICER reverberation 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 dissertation, I will present the X-ray spectral modeling results from each AGN in the context of understanding their geometries and how they affect their host galaxies.
Recommended Citation
Partington, Ethan Rhiannon, "The X-Ray/uv Connection In Active Galactic Nuclei" (2024). Wayne State University Dissertations. 4082.
https://digitalcommons.wayne.edu/oa_dissertations/4082