HARD X-RAY LAGS IN ACTIVE GALACTIC NUCLEI: TESTING THE DISTANT REVERBERATION HYPOTHESIS WITH NGC 6814

Journal Article · Sun Nov 10 04:00:00 EST 2013 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/777/2/L23· OSTI ID:22215381

Walton, D. J.; Harrison, F. A. ^[1]; Zoghbi, A.; Reynolds, C. S. ^[2]; Cackett, E. M. ^[3]; Uttley, P. ^[4]; Fabian, A. C.; Kara, E. ^[5]; Miller, J. M.; Reis, R. C. ^[6]

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1. Cahill Centre for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)
2. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
3. Department of Physics and Astronomy, Wayne State University, Detroit, MI 48201 (United States)
4. Astronomical Institute Anton Pannekoek, University of Amsterdam, Postbus 94249, NL-1090 GE Amsterdam (Netherlands)
5. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA (United Kingdom)
6. Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)

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.

• OSTI ID: 22215381
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 777; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
BLACK HOLES
EMISSION
GALAXIES
GALAXY NUCLEI
HARD X RADIATION
HYPOTHESIS
ORIGIN
REFLECTION
X-RAY SPECTRA