Year: 2025
Type: article
Abstract: We present the first systematic study of short-timescale X-ray variability in radio-quiet active galactic nuclei (AGN), utilizing archival Chandra observations of approximately 3000 broad-line AGN selected from the Sloan Digital Sky Survey and Dark Energy Spectroscopic Instrument spectroscopic surveys. We identify 14 AGN exhibiting rapid (on timescales of tens of kiloseconds) X-ray flux variations by factors of 2 or more that are statistically significant ( p ≤ 6 × 10 −4 ), indicative of fast coronal variability. By converting minimum variability timescales to light-crossing times, we place upper limits on the sizes of the variable coronal regions, finding typical scales of ≲10 −4 pc. The coronal variable region size upper limits of an AGN in our sample are found to be much smaller than the typical coronal sizes inferred from microlensing, suggesting that its corona is composed of localized, transient structures rather than smooth, homogeneous plasmas. Such efficient magnetic energy dissipation in compact volumes is consistent with expectations for magnetically dominated coronae and is supported by recent general relativistic magnetohydrodynamic simulations. Future high-throughput X-ray observatories will enable the detection of even faster coronal variability, providing direct constraints on the physical mechanisms driving plasma energization and flux fluctuation near supermassive black holes. Our results suggest that luminous AGN hosting massive black holes are prime targets for probing the small-scale structure and dynamics of AGN coronae.
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,400
Funders: National Science Foundation, U.S. Department of Energy, National Aeronautics and Space Administration, Alfred P. Sloan Foundation, Gordon and Betty Moore Foundation, Consejo Nacional de Ciencia y Tecnología, Ministerio de Ciencia e Innovación, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Office of Science, Science and Technology Facilities Council, Division of Astronomical Sciences, Lawrence Berkeley National Laboratory
Awards: G1044631029, G1079818582, G1143651532, G1286236842, G1632040200, G1813527838, G1863003419, G229706147, G3677525350, G419881185, G42916606, G4501827968, G4917691183, G498139845, G5004724115, G6652958823, G6876926712, Management and Operations of the National Optical Astronomy Observatory, G7354628648, G8060444232, G8231715376
OpenAlex ID: W7116696622