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Swift Monitoring of NGC 4151: Evidence for a Second X-Ray/UV Reprocessing

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.; Bontà, E. Dalla; Emmanoulopoulos, D.; Evans, P.; Jaimes, R. Figuera; 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.

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R. Edelson

J. Gelbord

E. Cackett

S. Connolly

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 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


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.


Edelson, R., Gelbord, J., Cackett, E., Connolly, S., Done, C., Fausnaugh, M., …Zheng, W. (2017). Swift Monitoring of NGC 4151: Evidence for a Second X-Ray/UV Reprocessing. Astrophysical Journal, 840(1), Article 41.

Journal Article Type Article
Acceptance Date Mar 18, 2017
Online Publication Date May 3, 2017
Publication Date May 3, 2017
Deposit Date Jul 5, 2017
Publicly Available Date Jul 5, 2017
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 840
Issue 1
Article Number 41


Published Journal Article (1.1 Mb)

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© 2017. The American Astronomical Society. All rights reserved.

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