Recent intensive monitoring campaigns of active galactic nuclei (AGN) have provided simultaneous X-ray, UV, and optical data of unprecedented quality. The observations reveal a strong correlation between the UV and optical variability, but a weaker correlation between the X-ray and UV bands, challenging the standard X-ray reprocessing scenario. We revisit the X-ray/UV connection in NGC 5548 by fitting archival 2014 HST and Swift/XRT light curves assuming X-ray reverberation from a dynamically evolving X-ray corona. Our results show that, as long as the corona height, photon index and power vary over time, X-ray reverberation can explain the observed UV and optical variability within 2% and 5%, respectively (on average). The evolution of the best-fit parameters suggests that fast changes in coronal geometry and energetics on a time scale of days are required to explain the observed variability.
@article{arxiv.2512.05739,
title = {The X-ray/UV Connection in NGC 5548: A Rapidly Varying Corona},
author = {M. Papoutsis and I. E. Papadakis and C. Panagiotou and E. Kammoun and M. Dovciak},
journal= {arXiv preprint arXiv:2512.05739},
year = {2026}
}
Comments
7 pages, 4 figures, Accepted for publication in Astronomy & Astrophysics