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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 on Hubble Space Telescope

  • Author(s): De Rosa, G
  • Peterson, BM
  • Ely, J
  • Kriss, GA
  • Crenshaw, DM
  • Horne, K
  • Korista, KT
  • Netzer, H
  • Pogge, RW
  • Arévalo, P
  • Barth, AJ
  • Bentz, MC
  • Brandt, WN
  • Breeveld, AA
  • Brewer, BJ
  • Dalla Bontá, E
  • Lorenzo-Cáceres, AD
  • Denney, KD
  • Dietrich, M
  • Edelson, R
  • Evans, PA
  • Fausnaugh, MM
  • Gehrels, N
  • Gelbord, JM
  • Goad, MR
  • Grier, CJ
  • Grupe, D
  • Hall, PB
  • Kaastra, J
  • Kelly, BC
  • Kennea, JA
  • Kochanek, CS
  • Lira, P
  • Mathur, S
  • McHardy, IM
  • Nousek, JA
  • Pancoast, A
  • Papadakis, I
  • Pei, L
  • Schimoia, JS
  • Siegel, M
  • Starkey, D
  • Treu, T
  • Uttley, P
  • Vaughan, S
  • Vestergaard, M
  • Villforth, C
  • Yan, H
  • Young, S
  • Zu, Y
  • et al.

© 2015. The American Astronomical Society. All rights reserved. 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.

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