Swift monitoring of NGC 4151 : evidence for a second X-ray/UV reprocessing
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.
Citation
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 . https://doi.org/10.3847/1538-4357/aa6890
Publication
Astrophysical Journal
Status
Peer reviewed
ISSN
0004-637XType
Journal article
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