Space Telescope and Optical Reverberation Mapping Project VI: reverberating Disk Models for NGC 5548

TL;DR

This study models the accretion disk of NGC 5548 using multiwavelength reverberation mapping data, revealing its temperature structure, inclination, and the limited role of X-ray variability in driving UV/optical changes.

Contribution

It introduces a detailed reverberating disk model for NGC 5548 that constrains disk parameters and examines the connection between X-ray and UV/optical variability.

Findings

Disk inclination and temperature profile were estimated.

X-ray variability poorly correlates with UV/optical variability.

Decomposed spectra are below standard blackbody expectations.

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 to 9157 angstroms) 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, temperature T1 at 1 light day from the black hole, and a temperature-radius slope, alpha. 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/LEdd = 0.1