Space Telescope and Optical Reverberation Mapping Project.VI. Reverberating Disk Models for NGC 5548
Im, M.; Geier, S.; Zheng, W.; Brandt, W. N.; Kriss, G. A.; Ely, J.; Kochanek, C. S.; Filippenko, A. V.; Crenshaw, D. M.; Gehrels, N.; Vestergaard, M.; Rix, H. -W.; Horne, Keith; Pott, J. -U.; Peterson, B. M.; Dietrich, M.; Korista, K. T.; Pogge, R. W.; Uttley, P.; Kennea, J. A.; Cackett, E. M.; Arévalo, P.; Borman, G. A.; Klimanov, S. A.; Nazarov, S. V.; Gorjian, V.; Grupe, D.; Mathur, S.; Lira, P.; Young, S.; Goad, M. R.; Norris, R. P.; Evans, P. A.; Croxall, K. V.; Fausnaugh, M. M.; Kaspi, S.; Sergeev, S. G.; Kaastra, J.; Pancoast, A.; Barth, A. J.; De Rosa, G.; Bentz, M. C.; Dalla Bontà, E.; Grier, C. J.; Anderson, M. D.; Boroson, T. A.; Bottorff, M. C.; Breeveld, A. A.; Carini, M. T.; De Lorenzo-Cáceres, A.; Denney, K. D.; Edelson, R.; Efimova, N. V.; Flatland, K.; Gelbord, J. M.; Gonzalez, L.; Hall, P. B.; Hicks, S.; Hutchison, T.; Jensen, J. J.; Joner, M. D.; Jones, J.; Kim, M.; Kim, S. C.; Lee, J. C.; Leonard, D. C.; MacInnis, F.; Manne-Nicholas, E. R.; McHardy, I. M.; Nousek, J. A.; Okhmat, D. N.; Parks, J. R.; Pei, L.; Rafter, S. E.; Saylor, D. A.; Schimoia, J. S.; Spencer, M.; Starkey, D.; Sung, H. -I.; Turner, C. S.; Villforth, C.; Weiss, Y.; Woo, J. -H.; Yan, H.; Zu, Y.; Siegel, M. H.; Bazhaw, C.; Horenstein, D.; Kelly, B. C.; Montouri, C.; Musso, R.; Schnülle, K.; Teems, K. G.
United Kingdom, United States, Chile, Russia, Italy, Spain, Canada, South Korea, Denmark, Netherlands, Israel, Brazil, Germany
Abstract
We conduct a multiwavelength continuum variability study of the Seyfert 1 galaxy NGC 5548 to investigate the temperature structure of its accretion disk. The 19 overlapping continuum light curves (1158 \mathringA to 9157 \mathringA ) combine simultaneous Hubble Space Telescope, Swift, and ground-based observations over a 180 day period from 2014 January to July. Light-curve variability is interpreted as the reverberation response of the accretion disk to irradiation by a central time-varying point source. Our model yields the disk inclination I=36^\circ +/- 10^\circ , temperature {T}1=(44+/- 6)× {10}3 K at 1 light day from the black hole, and a temperature-radius slope (T\propto {r}-α ) of α =0.99+/- 0.03. We also infer the driving light curve and find that it correlates poorly with both the hard and soft X-ray light curves, suggesting that the X-rays alone may not drive the ultraviolet and optical variability over the observing period. We also decompose the light curves into bright, faint, and mean accretion-disk spectra. These spectra lie below that expected for a standard blackbody accretion disk accreting at L/{L}{Edd}=0.1.