Departures from standard disc predictions in intensive ground-based monitoring of three AGNs

作者：D. González–Buitrago, Aaron J. Barth, Rick Edelson, J V Hernández Santisteban, K. Horne, Thomas Schmidt, Yanrong Li, Hengxiao Guo, M. D. Joner, Edward M. Cackett, J. M. Gelbord, Misty C. Bentz, W. N. Brandt, M. R. Goad, K. T. Korista, M. Vestergaard, C. Villforth, A. A. Breeveld, Thomas G. Brink, E. M. Corsini, E. Dalla Bontà, G. J. Ferland, A. V. Filippenko, Ma. T. García-Díaz, M. K. Hallum, J. Chuck Horst, M Kim, Y. Krongold, J. Krüger, Bertram Kühn, Sahana Kumar, M. Mehdipour, L. Morelli, Smita Mathur, H. Netzer, P. Ochner, Ilaria Pagotto, A. Pizzella, David J. Sand, A. Siviero, M. Spencer, H Sung, S. Vaughan, Hartmut Winkler, W Zheng · 发表于：Monthly Notices of the Royal Astronomical Society · 年份：2025 · DOI：10.1093/mnras/staf1334 · 被引用次数：4 · 研究领域：GNSS positioning and interference、Gamma-ray bursts and supernovae、Astrophysics and Cosmic Phenomena

ABSTRACT We present ground-based multiband light curves of the AGN Mrk 509, NGC 4151, and NGC 4593 obtained contemporaneously with Swift monitoring. We measure cross-correlation lags relative to Swift UVW2 (1928 Å) and test the standard prediction for disc reprocessing, which assumes a geometrically thin optically thick accretion disc where continuum interband delays follow the relation $\tau (\lambda) \propto \lambda ^{4/3}$. For Mrk 509 the 273-d Swift campaign gives well-defined lags that increase with wavelength as $\tau (\lambda)\propto \lambda ^{2.17\pm 0.2}$, steeper than the thin-disc prediction, and the optical lags are a factor of $\sim 5$ longer than expected for a simple disc-reprocessing model. This ‘disc-size discrepancy’ as well as excess lags in the u and r bands (which include the Balmer continuum and H $\alpha$, respectively) suggest a mix of short lags from the disc and longer lags from nebular continuum originating in the broad-line region. The shorter Swift campaigns, 69 d on NGC 4151 and 22 d on NGC 4593, yield less well-defined shorter lags $< 2$ d. The NGC 4593 lags are consistent with $\tau (\lambda) \propto \lambda ^{4/3}$ but with uncertainties too large for a strong test. For NGC 4151 the Swift lags match $\tau (\lambda) \propto \lambda ^{4/3}$, with a small U-band excess, but the ground-based lags in the r, i, and z bands are significantly shorter than the B and g lags, and also shorter than expected from the thin-disc prediction. The inter...