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. CrawfordElena Dalla Bontà, 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

Research output: Contribution to journalArticlepeer-review

119 Scopus citations

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 languageEnglish
Article number41
JournalAstrophysical Journal
Volume840
Issue number1
DOIs
StatePublished - 1 May 2017

Funding

FundersFunder number
TABASGO Foundation
David and Lucile Packard Foundation
National Research Foundation
UK Research and Innovation
Not addedST/P002218/1, ST/P006892/1, ST/L005654/1, ST/P000541/1, ST/N000811/1, ST/M003035/1, AST-1253702, ST/M001296/1
National Science FoundationAST-1412693, 1412315, 1412155, 1253702, 1210311
Christopher R. Redlich FundAST-1412315, AST-1009571, AST-1210311
National Aeronautics and Space AdministrationNNH13CH61C, NNX13AC63G, NNX13AE99G, NNX13AC26G
UK Space AgencyAST-1211916
Natur og Univers, Det Frie ForskningsrådDFF 4002-00275

    Keywords

    • galaxies: Seyfert
    • galaxies: active
    • galaxies: individual (NGC 4151)
    • galaxies: nuclei

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