The First Swift Intensive AGN Accretion Disk Reverberation Mapping Survey

R. Edelson, J. Gelbord, E. Cackett, B. M. Peterson, K. Horne, A. J. Barth, D. A. Starkey, M. Bentz, W. N. Brandt, M. Goad, M. Joner, K. Korista, H. Netzer, K. Page, P. Uttley, S. Vaughan, A. Breeveld, S. B. Cenko, C. Done, P. EvansM. Fausnaugh, G. Ferland, D. Gonzalez-Buitrago, J. Gropp, D. Grupe, J. Kaastra, J. Kennea, G. Kriss, S. Mathur, M. Mehdipour, D. Mudd, J. Nousek, T. Schmidt, M. Vestergaard, C. Villforth

Research output: Contribution to journalArticlepeer-review

71 Scopus citations


Swift intensive accretion disk reverberation mapping of four AGN yielded light curves sampled ∼200-350 times in 0.3-10 keV X-ray and six UV/optical bands. Uniform reduction and cross-correlation analysis of these data sets yields three main results: (1) The X-ray/UV correlations are much weaker than those within the UV/optical, posing severe problems for the lamp-post reprocessing model in which variations in a central X-ray corona drive and power those in the surrounding accretion disk. (2) The UV/optical interband lags are generally consistent with as predicted by the centrally illuminated thin accretion disk model. While the average interband lags are somewhat larger than predicted, these results alone are not inconsistent with the thin disk model given the large systematic uncertainties involved. (3) The one exception is the U band lags, which are on average a factor of ∼2.2 larger than predicted from the surrounding band data and fits. This excess appears to be due to diffuse continuum emission from the broad-line region (BLR). The precise mixing of disk and BLR components cannot be determined from these data alone. The lags in different AGN appear to scale with mass or luminosity. We also find that there are systematic differences between the uncertainties derived by JAVELIN versus more standard lag measurement techniques, with JAVELIN reporting smaller uncertainties by a factor of 2.5 on average. In order to be conservative only standard techniques were used in the analyses reported herein.

Original languageEnglish
Article number123
JournalAstrophysical Journal
Issue number2
StatePublished - Jan 10 2019

Bibliographical note

Funding Information:
K.H. acknowledges support from STFC grant ST/R000824/1. A. B. and K.P. acknowledge support from the UK Space Agency. M.C.B. gratefully acknowledges support from the National Science Foundation through CAREER grant AST-1253702. C.D. acknowledges the Science and Technology Facilities Council (STFC) through grant ST/P000541/1 for support. M.V. gratefully acknowledges support from the Independent Research Fund Denmark via grant number DFF 4002-00275. SRON is supported financially by NWO, the Netherlands Organization for Scientific Research.

Funding Information:
The authors note the crucial role played in this research by Neil Gehrels, the late director of Swift: without his decision to allow full 6-filter UVOT monitoring for the duration of these campaigns, these results would not have been possible. We also appreciate Ian McHardy’s leadership of the third IDRM campaign, on NGC 4593, and Chris Kochanek’s input on JAVELIN. R.E. and J.M.G. gratefully acknowledge support from NASA under the ADAP award 80NSSC17K0126. Research by A.J.B. is supported by NSF grant AST-1412693.

Publisher Copyright:
© 2019. The American Astronomical Society. All rights reserved.


  • galaxies: Seyfert
  • galaxies: active
  • galaxies: nuclei

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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