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.
Original language | English |
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Article number | 41 |
Journal | Astrophysical Journal |
Volume | 840 |
Issue number | 1 |
DOIs | |
State | Published - 1 May 2017 |
Funding
Funders | Funder number |
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TABASGO Foundation | |
David and Lucile Packard Foundation | |
National Research Foundation | |
UK Research and Innovation | |
Not added | ST/P002218/1, ST/P006892/1, ST/L005654/1, ST/P000541/1, ST/N000811/1, ST/M003035/1, AST-1253702, ST/M001296/1 |
National Science Foundation | AST-1412693, 1412315, 1412155, 1253702, 1210311 |
Christopher R. Redlich Fund | AST-1412315, AST-1009571, AST-1210311 |
National Aeronautics and Space Administration | NNH13CH61C, NNX13AC63G, NNX13AE99G, NNX13AC26G |
UK Space Agency | AST-1211916 |
Natur og Univers, Det Frie Forskningsråd | DFF 4002-00275 |
Keywords
- galaxies: Seyfert
- galaxies: active
- galaxies: individual (NGC 4151)
- galaxies: nuclei