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.

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 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.

Citation

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. https://doi.org/10.3847/1538-4357/aa6890

• 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
• DOI: https://doi.org/10.3847/1538-4357/aa6890