Swift monitoring of NGC 4151: Evidence for a Second X-ray/UV Reprocessing

R. Edelson; J. Gelbord; E. Cackett; S. Connolly; C. Done; M. Fausnaugh; E. Gardner; N. Gehrels; M. Goad; K. Horne; I. McHardy; B. M. Peterson; S. Vaughan; M. Vestergaard; A. Breeveld; A. J. Barth; M. Bentz; M. Bottorff; W. N. Brandt; S. M. Crawford; E. Dalla Bonta; D. Emmanoulopoulos; P. Evans; R. Figuera Jaimes; A. V. Filippenko; G. Ferland; D. Grupe; M. Joner; J. Kennea; K. T. Korista; H. A. Krimm; G. Kriss; D. C. Leonard; S. Mathur; H. Netzer; J. Nousek; K. Page; E. Romero-Colmenero; M. Siegel; D. A. Starkey; T. Treu; H. A. Vogler; H. Winkler; W. Zheng

doi:10.3847/1538-4357/aa6890

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arXiv · 1703.06901

Swift monitoring of NGC 4151: Evidence for a Second X-ray/UV Reprocessing

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Abstract

Swift monitoring of NGC 4151 with ~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 A). 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 day. 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.

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R. Edelson, J. Gelbord, E. Cackett, S. Connolly, C. Done, M. Fausnaugh, E. Gardner, N. Gehrels, M. Goad, K. Horne, I. McHardy, B. M. Peterson, S. Vaughan, M. Vestergaard, A. Breeveld, A. J. Barth, M. Bentz, M. Bottorff, W. N. Brandt, S. M. Crawford, E. Dalla Bonta, D. Emmanoulopoulos, P. Evans, R. Figuera Jaimes, A. V. Filippenko, G. Ferland, D. Grupe, M. Joner, J. Kennea, K. T. Korista, H. A. Krimm, G. Kriss, D. C. Leonard, S. Mathur, H. Netzer, J. Nousek, K. Page, E. Romero-Colmenero, M. Siegel, D. A. Starkey, T. Treu, H. A. Vogler, H. Winkler, W. Zheng. 2017-03-20. Swift monitoring of NGC 4151: Evidence for a Second X-ray/UV Reprocessing. https://doi.org/10.3847/1538-4357/aa6890

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