Swift monitoring of NGC 4151 : evidence for a second X-ray/UV reprocessing
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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.
Edelson , R , Gelbord , J , Cackett , E , Connolly , S , Done , C , Fausnaugh , M , Gardner , E , Gehrels , N , Goad , M , Horne , K , McHardy , I , Peterson , B M , Vaughan , S , Vestergaard , M , Breeveld , A , Barth , A J , Bentz , M , Bottorff , M , Brandt , W N , Crawford , S M , Bonta , E D , Emmanoulopoulos , D , Evans , P , Jaimes , R F , Filippenko , A V , Ferland , G , Grupe , D , Joner , M , Kennea , J , Korista , K T , Krimm , H A , Kriss , G , Leonard , D C , Mathur , S , Netzer , H , Nousek , J , Page , K , Romero-Colmenero , E , Siegel , M , Starkey , D A , Treu , T , Vogler , H A , Winkler , H & Zheng , W 2017 , ' Swift monitoring of NGC 4151 : evidence for a second X-ray/UV reprocessing ' Astrophysical Journal , vol 840 , no. 1 , 41 . DOI: 10.3847/1538-4357/aa6890
© 2017, American Astronomical Society. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at iopscience.iop.org / https://doi.org/10.3847/1538-4357/aa6890
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