Space Telescope and Optical Reverberation Mapping Project. VIII. Time
  Variability of Emission and Absorption in NGC 5548 Based on Modeling the
  Ultraviolet Spectrum
  We model the ultraviolet spectra of the Seyfert 1 galaxy NGC~5548 obtained
with the Hubble Space Telescope during the 6-month reverberation-mapping
campaign in 2014. Our model of the emission from NGC 5548 corrects for
overlying absorption and deblends the individual emission lines. Using the
modeled spectra, we measure the response to continuum variations for the
deblended and absorption-corrected individual broad emission lines, the
velocity-dependent profiles of Ly$\alpha$ and C IV, and the narrow and broad
intrinsic absorption features. We find that the time lags for the corrected
emission lines are comparable to those for the original data. The
velocity-binned lag profiles of Ly$\alpha$ and C IV have a double-peaked
structure indicative of a truncated Keplerian disk. The narrow absorption lines
show delayed response to continuum variations corresponding to recombination in
gas with a density of $\sim 10^5~\rm cm^{-3}$. The high-ionization narrow
absorption lines decorrelate from continuum variations during the same period
as the broad emission lines. Analyzing the response of these absorption lines
during this period shows that the ionizing flux is diminished in strength
relative to the far-ultraviolet continuum. The broad absorption lines
associated with the X-ray obscurer decrease in strength during this same time
interval. The appearance of X-ray obscuration in $\sim\,2012$ corresponds with
an increase in the luminosity of NGC 5548 following an extended low state. We
suggest that the obscurer is a disk wind triggered by the brightening of NGC
5548 following the decrease in size of the broad-line region during the
preceding low-luminosity state.
