Continuum Reverberation Mapping of the Accretion Disks in Two Seyfert 1 Galaxies

M. M. Fausnaugh, D. A. Starkey, Keith Horne, C. S. Kochanek, B. M. Peterson, M. C. Bentz, K. D. Denney, C. J. Grier, D. Grupe, R. W. Pogge, G. DeRosa, S. M. Adams, A. J. Barth, Thomas G. Beatty, A. Bhattacharjee, G. A. Borman, T. A. Boroson, M. C. Bottorff, Jacob E. Brown, Jonathan S. Brown, M. S. Brotherton, C. T. Coker, S. M. Crawford, K. V. Croxall, Sarah Eftekharzadeh, Michael Eracleous, M. D. Joner, C. B. Henderson, T. W. -S. Holoien, T. Hutchison, Shai Kaspi, S. Kim, Anthea L. King, Miao Li, Cassandra Lochhaas, Zhiyuan Ma, F. MacInnis, E. R. Manne-Nicholas, M. Mason, Carmen Montuori, Ana Mosquera, Dale Mudd, R. Musso, S. V. Nazarov, M. L. Nguyen, D. N. Okhmat, ChristopherA. Onken, B. Ou-Yang, A. Pancoast, L. Pei, Matthew T. Penny, Radosław Poleski, Stephen Rafter, E. Romero-Colmenero, Jessie Runnoe, David J. Sand, Jaderson S. Schimoia, S. G. Sergeev, B. J. Shappee, Gregory V. Simonian, Garrett Somers, M. Spencer, Daniel J. Stevens, Jamie Tayar, T. Treu, Stefano Valenti, J. VanSaders, S. VillanuevaJr., C. Villforth, Yaniv Weiss, H. Winkler, W. Zhu

Published 2018-01-29Version 1

We present optical continuum lags for two Seyfert 1 galaxies, MCG+08-11-011 and NGC 2617, using monitoring data from a reverberation mapping campaign carried out in 2014. Our light curves span the ugriz filters over four months, with median cadences of 1.0 and 0.6 days for MCG+08-11-011 and NGC\,2617, respectively, combined with roughly daily X-ray and near-UV data from Swift for NGC 2617. We find lags consistent with geometrically thin accretion-disk models that predict a lag-wavelength relation of $\tau \propto \lambda^{4/3}$. However, the observed lags are larger than predictions based on standard thin-disk theory by factors of 3.3 for MCG+08-11-011 and 2.3 for NGC\,2617. These differences can be explained if the mass accretion rates are larger than inferred from the optical luminosity by a factor of 4.3 in MCG+08-11-011 and a factor of 1.3 in NGC\,2617, although uncertainty in the SMBH masses determines the significance of this result. While the X-ray variability in NGC\,2617 precedes the UV/optical variability, the long 2.6 day lag is problematic for coronal reprocessing models.