SPACE TELESCOPE AND OPTICAL REVERBERATION MAPPING PROJECT. II. SWIFT AND HST REVERBERATION MAPPING OF THE ACCRETION DISK OF NGC 5548

By R. Edelson, J. Gelbord, K. Horne, I. McHardy, B. Peterson, P. Arévalo, A. Breeveld, G. D. Rosa, P. A. Evans, M. Goad and 40 more. 2015

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Recent 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 max = 0.57 − 0.90 ?> ) and the clearest measurement to date of interband lags. These lags are well-fit by a τ ∝ λ 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 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.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

Active galactic nuclei: what’s in a name? (2017, background): “…BHXRBs; the fact that the inner/outer disk and the BLR directly respond to continuum variations as inferred from results of X-ray (Fabian et al. 2009; Zoghbi et al. 2012; De Marco et al. 2013; Kara et al. 2016) and UV/optical reverberation mapping (e.g. Peterson et al. 2004; Edelson et al. 2015).”
The Sloan Digital Sky Survey Reverberation Mapping Project: Hα and Hβ Reverberation Measurements from First-year Spectroscopy and Photometry (2017, background): “Recent work has indicated that the optical continuum-emitting region can have a significant lag relative to the UV (Collier et al. 1998; Sergeev et al. 15 2005; McHardy et al. 2014; Shappee et al. 2014; Edelson et al. 2015; Fausnaugh et al. 2016).”
A systematic search for changing-look quasars in SDSS (2015, background): “…by reprocessing of EUV or X-ray light (e.g., c© 2015 The Authors Collier et al. 1998; Sergeev et al. 2005; Cackett et al. 2007; Shappee et al. 2014; Edelson et al. 2015) but this may be due to inner cloud reprocessing rather than the disc itself (Lawrence 2012), and the reliability of the…”