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 \mathrm { \AA } to 9157 \mathrm { \AA } ) combine simultaneous HST , 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 } \pm 10 ^ { \circ } , temperature T _ { 1 } = \left ( 44 \pm 6 \right ) \times 10 ^ { 3 } K at 1 light day from the black hole , and a temperature-radius slope ( T \propto r ^ { - \alpha } ) of \alpha = 0.99 \pm 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 .