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American Astronomical Society, Astrophysical Journal, 1(806), p. 128, 2015

DOI: 10.1088/0004-637x/806/1/128

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Space Telescope and Optical Reverberation Mapping Project. I. Ultraviolet Observations of the Seyfert 1 Galaxy NGC 5548 With the Cosmic Origins Spectrograph Onhubble Space Telescope

Journal article published in 2015 by G. De Rosa, B. M. Peterson ORCID, J. Ely, G. A. Kriss, D. M. Crenshaw, Keith Horne, K. T. Korista, H. Netzer, R. W. Pogge ORCID, P. Arévalo, A. J. Barth ORCID, M. C. Bentz, W. N. Brandt, A. A. Breeveld, B. J. Brewer and other authors.
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

We describe the first results from a six-month long reverberation-mapping experiment in the ultraviolet based on 171 observations of the Seyfert 1 galaxy NGC 5548 with the Cosmic Origins Spectrograph on the Hubble Space Telescope. Significant correlated variability is found in the continuum and broad emission lines, with amplitudes ranging from ~30% to a factor of two in the emission lines and a factor of three in the continuum. The variations of all the strong emission lines lag behind those of the continuum, with He ii λ1640 lagging behind the continuum by ~2.5 days and Lyα λ1215, C iv λ1550, and Si iv λ1400 lagging by ~5–6 days. The relationship between the continuum and emission lines is complex. In particular, during the second half of the campaign, all emission-line lags increased by a factor of 1.3–2 and differences appear in the detailed structure of the continuum and emission-line light curves. Velocity-resolved cross-correlation analysis shows coherent structure in lag versus line of sight velocity for the emission lines; the high-velocity wings of C iv respond to continuum variations more rapidly than the line core, probably indicating higher velocity broad-line region clouds at smaller distances from the central engine. The velocity-dependent response of Lyα, however, is more complex and will require further analysis. ; Peer-reviewed ; Publisher Version