1. Swift Monitoring of NGC 4151: Evidence for a Second X-Ray/UV Reprocessing
- Author
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Edelson, R, Gelbord, J, Cackett, E, Connolly, S, Done, C, Fausnaugh, M, Gardner, E, Gehrels, N, Goad, M, Horne, K, McHardy, I, Peterson, BM, Vaughan, S, Vestergaard, M, Breeveld, A, Barth, AJ, Bentz, M, Bottorff, M, Brandt, WN, Crawford, SM, Bontà, E Dalla, Emmanoulopoulos, D, Evans, P, Jaimes, R Figuera, Filippenko, AV, Ferland, G, Grupe, D, Joner, M, Kennea, J, Korista, KT, Krimm, HA, Kriss, G, Leonard, DC, Mathur, S, Netzer, H, Nousek, J, Page, K, Romero-Colmenero, E, Siegel, M, Starkey, DA, Treu, T, Vogler, HA, Winkler, H, and Zheng, W
- Subjects
galaxies: active ,galaxies: individual ,galaxies: nuclei ,galaxies: Seyfert ,astro-ph.HE ,Astronomical and Space Sciences ,Atomic ,Molecular ,Nuclear ,Particle and Plasma Physics ,Physical Chemistry (incl. Structural) ,Astronomy & Astrophysics - Abstract
Swift monitoring of NGC 4151 with an ∼6 hr sampling over a total of 69 days in early 2016 is used to construct light curves covering five bands in the X-rays (0.3-50 keV) and six in the ultraviolet (UV)/optical (1900-5500 Å). The three hardest X-ray bands (>2.5 keV) are all strongly correlated with no measurable interband lag, while the two softer bands show lower variability and weaker correlations. The UV/optical bands are significantly correlated with the X-rays, lagging ∼3-4 days behind the hard X-rays. The variability within the UV/optical bands is also strongly correlated, with the UV appearing to lead the optical by ∼0.5-1 days. This combination of ≳3 day lags between the X-rays and UV and ≲1 day lags within the UV/optical appears to rule out the "lamp-post" reprocessing model in which a hot, X-ray emitting corona directly illuminates the accretion disk, which then reprocesses the energy in the UV/optical. Instead, these results appear consistent with the Gardner & Done picture in which two separate reprocessings occur: first, emission from the corona illuminates an extreme-UV-emitting toroidal component that shields the disk from the corona; this then heats the extreme-UV component, which illuminates the disk and drives its variability.
- Published
- 2017