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Swift monitoring of NGC 4151 : evidence for a second X-ray/UV reprocessing.

Edelson, R. and Gelbord, J. and Cackett, E. and Connolly, S. and Done, C. and Fausnaugh, M. and Gardner, E. and Gehrels, N. and Goad, M. and Horne, K. and McHardy, I. and Peterson, B. M. and Vaughan, S. and Vestergaard, M. and Breeveld, A. and Barth, A. J. and Bentz, M. and Bottorff, M. and Brandt, W. N. and Crawford, S. M. and Bontà, E. Dalla and Emmanoulopoulos, D. and Evans, P. and Jaimes, R. Figuera and Filippenko, A. V. and Ferland, G. and Grupe, D. and Joner, M. and Kennea, J. and Korista, K. T. and Krimm, H. A. and Kriss, G. and Leonard, D. C. and Mathur, S. and Netzer, H. and Nousek, J. and Page, K. and Romero-Colmenero, E. and Siegel, M. and Starkey, D. A. and Treu, T. and Vogler, H. A. and Winkler, H. and Zheng, W. (2017) 'Swift monitoring of NGC 4151 : evidence for a second X-ray/UV reprocessing.', Astrophysical journal., 840 (1). p. 41.


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 gsim3 day lags between the X-rays and UV and lesssim1 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.

Item Type:Article
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Publisher statement:© 2017. The American Astronomical Society. All rights reserved.
Date accepted:18 March 2017
Date deposited:05 July 2017
Date of first online publication:03 May 2017
Date first made open access:05 July 2017

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