SPACE TELESCOPE AND OPTICAL REVERBERATION MAPPING PROJECT. I. ULTRAVIOLET OBSERVATIONS OF THE SEYFERT 1 GALAXY NGC 5548 WITH THE COSMIC ORIGINS SPECTROGRAPH ON HUBBLE SPACE TELESCOPE

• Published in: The Astrophysical journal 2015-06, Vol.806 (1), p.1-15
• Main Authors: Rosa, G. De, Peterson, B. M., Ely, J., Kriss, G. A., Crenshaw, D. M., Horne, Keith, Korista, K. T., Netzer, H., Pogge, R. W., Arévalo, P., Barth, A. J., Bentz, M. C., Brandt, W. N., Breeveld, A. A., Brewer, B. J., Dalla Bontà, E., Lorenzo-Cáceres, A. De, Denney, K. D., Dietrich, M., Edelson, R., Evans, P. A., Fausnaugh, M. M., Gehrels, N., Gelbord, J. M., Goad, M. R., Grier, C. J., Grupe, D., Hall, P. B., Kaastra, J., Kelly, B. C., Kennea, J. A., Kochanek, C. S., Lira, P., Mathur, S., McHardy, I. M., Nousek, J. A., Pancoast, A., Papadakis, I., Pei, L., Schimoia, J. S., Siegel, M., Starkey, D., Treu, T., Uttley, P., Vaughan, S., Vestergaard, M., Villforth, C., Yan, H., Young, S., Zu, Y.
• Format: Article
• Language: English
• Subjects: ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Continuums; COSMIC DUST; DISTANCE; EMISSION; Galaxies; galaxies: active; galaxies: individual (NGC 5548); galaxies: nuclei; galaxies: Seyfert; GALAXY NUCLEI; Hubble Space Telescope; Origins; SEYFERT GALAXIES; SPACE; Spectrographs; TELESCOPES; Ultraviolet; ULTRAVIOLET RADIATION; VELOCITY
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.1088/0004-637X/806/1/128

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 lagging behind the continuum by ∼2.5 days and Ly , C iv , and Si iv 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 Ly , however, is more complex and will require further analysis.