Abstract :
We will review the recent discoveries made by incorporating the Neutron Star Interior Composition ExploreR (NICER) into reverberation mapping experiments on X-ray bright AGN. The AGNs Fairall 9 and Mrk 817 were targeted by NICER, Swift, and other space- and ground-based observatories for the two longest coordinated multiwavelength AGN monitoring campaigns to date (>1,000 days). The analysis of NICER spectra taken at a two day cadence revealed new insights into the structure and heating mechanisms of the central black hole.
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.
Our 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 seminar, I will present the X-ray spectral modeling results from each AGN in the context of understanding their geometries and energetic properties.
