A Caltech Library Service

Hard X-Ray Lags in Active Galactic Nuclei: Testing the Distant Reverberation Hypothesis with NGC 6814

Walton, D. J. and Zoghbi, A. and Cackett, E. M. and Uttley, P. and Harrison, F. A. and Fabian, A. C. and Kara, E. and Miller, J. M. and Reis, R. C. and Reynolds, C. S. (2013) Hard X-Ray Lags in Active Galactic Nuclei: Testing the Distant Reverberation Hypothesis with NGC 6814. Astrophysical Journal Letters, 777 (2). Art. No. L23. ISSN 2041-8205.

PDF - Published Version
See Usage Policy.

PDF - Submitted Version
See Usage Policy.


Use this Persistent URL to link to this item:


We present an X-ray spectral and temporal analysis of the variable active galaxy NGC 6814, observed with Suzaku during 2011 November. Remarkably, the X-ray spectrum shows no evidence for the soft excess commonly observed amongst other active galaxies, despite its relatively low level of obscuration, and is dominated across the whole Suzaku bandpass by the intrinsic powerlaw-like continuum. Despite this, we clearly detect the presence of a low-frequency hard lag of ~1600 s between the 0.5-2.0 and 2.0-5.0 keV energy bands at greater than 6σ significance, similar to those reported in the literature for a variety of other active galactic nuclei (AGNs). At these energies, any additional emission from, e.g., a very weak, undetected soft excess, or from distant reflection must contribute less than 3% of the observed countrates (at 90% confidence). Given the lack of any significant continuum emission component other than the powerlaw, we can rule out models that invoke distant reprocessing for the observed lag behavior, which must instead be associated with this continuum emission. These results are fully consistent with a propagating fluctuation origin for the low-frequency hard lags, and with the interpretation of the high-frequency soft lags—a common feature seen in the highest quality AGN data with strong soft excesses—as reverberation from the inner accretion disk.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Walton, D. J.0000-0001-5819-3552
Zoghbi, A.0000-0002-0572-9613
Cackett, E. M.0000-0002-8294-9281
Harrison, F. A.0000-0003-2992-8024
Fabian, A. C.0000-0002-9378-4072
Kara, E.0000-0003-0172-0854
Additional Information:© 2013 American Astronomical Society. Received 2013 August 2; accepted 2013 October 1; published 2013 October 22. The authors thank the reviewer for useful feedback. This research has made use of data obtained from the Suzaku observatory, a collaborative mission between the space agencies of Japan (JAXA) and the USA (NASA). C.S.R. thanks support from NASA under grant NNX12AE13G.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Subject Keywords:black hole physics; galaxies: active; X-rays: individual (NGC 6814)
Issue or Number:2
Record Number:CaltechAUTHORS:20131203-081809632
Persistent URL:
Official Citation:Hard X-Ray Lags in Active Galactic Nuclei: Testing the Distant Reverberation Hypothesis with NGC 6814 D. J. Walton et al. 2013 ApJ 777 L23
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42785
Deposited By: Ruth Sustaita
Deposited On:03 Dec 2013 16:34
Last Modified:09 Mar 2020 13:19

Repository Staff Only: item control page