SPACE TELESCOPE AND OPTICAL REVERBERATION MAPPING PROJECT. II. SWIFT AND HST REVERBERATION MAPPING OF THE ACCRETION DISK OF NGC 5548
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posted on 2015-08-05, 11:42 authored by R. Edelson, J. M. Gelbord, K. Horne, I. M. McHardy, B. M. Peterson, P. Arevalo, A. A. Breeveld, G. De Rosa, P. A. Evans, Michael R. Goad, G. A. Kriss, W. N. Brandt, N. Gehrels, D. Grupe, J. A. Kennea, C. S. Kochanek, J. A. Nousek, I. Papadakis, M. Siegel, D. Starkey, P. Uttley, S. Vaughan, S. Young, A. J. Barth, M. C. Bentz, B. J. Brewer, D. M. Crenshaw, E. D. Bonta, A. De Lorenzo-Caceres, K. D. Denney, M. Dietrich, J. Ely, M. M. Fausnaugh, C. J. Grier, P. B. Hall, J. Kaastra, B. C. Kelly, K. T. Korista, P. Lira, S. Mathur, H. Netzer, A. Pancoast, L. Pei, R. W. Pogge, J. S. Schimoia, T. Treu, M. Vestergaard, C. Villforth, H. Yan, Y. ZuRecent intensive Swift monitoring of the Seyfert 1 galaxy NGC 5548 yielded 282 usable epochs over 125 days across six UV/optical bands and the X-rays. This is the densest extended active galactic nucleus (AGN) UV/optical continuum sampling ever obtained, with a mean sampling rate <0.5 day. Approximately daily Hubble Space Telescope UV sampling was also obtained. The UV/optical light curves show strong correlations (r[subscript: max] = 0.57-0.90) and the clearest measurement to date of interband lags. These lags are well-fit by a τ ∝ λ[superscript: 4/3] wavelength dependence, with a normalization that indicates an unexpectedly large disk radius of ~ 0.35 ± 0.05 lt-day at 1367 Å, assuming a simple face-on model. The U band shows a marginally larger lag than expected from the fit and surrounding bands, which could be due to Balmer continuum emission from the broad-line region as suggested by Korista and Goad. The UV/X-ray correlation is weaker (r[subscript: max] < 0.45) and less consistent over time. This indicates that while Swift is beginning to measure UV/optical lags in general agreement with accretion disk theory (although the derived size is larger than predicted), the relationship with X-ray variability is less well understood. Combining this accretion disk size estimate with those from quasar microlensing studies suggests that AGN disk sizes scale approximately linearly with central black hole mass over a wide range of masses.
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Astrophysical Journal, 2015, 806 (1), 129Author affiliation
/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and AstronomyVersion
- VoR (Version of Record)
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Astrophysical JournalPublisher
IOP Publishing LTDissn
0004-637Xeissn
1538-4357Acceptance date
2015-04-03Copyright date
2015Available date
2015-08-05Publisher DOI
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http://iopscience.iop.org/0004-637X/806/1/129/Language
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Science & TechnologyPhysical SciencesAstronomy & Astrophysicsgalaxies: activegalaxies: individual (NGC 5548)galaxies: nucleigalaxies: SeyfertACTIVE GALACTIC NUCLEIBROAD-LINE REGIONRADIUS-LUMINOSITY RELATIONSHIPX-RAYCONTINUUM EMISSIONSEYFERT-GALAXIESULTRAVIOLET/OPTICAL TELESCOPEEMITTING REGIONSMR 2251-178VARIABILITY