Evidence for Two Distinct Broad-Line Regions from Reverberation Mapping
  of PG 0026+129
  We report on the results of a new spectroscopic monitoring campaign of the
quasar PG 0026+129 at the Calar Alto Observatory 2.2m telescope from July 2017
to February 2020. Significant variations in the fluxes of the continuum and
broad-emission lines, including H$\beta$ and He II, were observed in the first
and third years, and clear time lags between them are measured. The broad
H$\beta$ line profile consists of two Gaussian components: an
intermediate-width H$\beta_{\rm IC}$ with a full width at half-maximum (FWHM)
of 1964$\pm$18 $\rm km~s^{-1}$ and another very broad H$\beta_{\rm VBC}$ with a
FWHM of 7570$\pm$83 $\rm km~s^{-1}$. H$\beta_{\rm IC}$ has long time lags of
$\sim$40--60 days in the rest frame, while H$\beta_{\rm VBC}$ shows nearly zero
time delay with respect to the optical continuum at 5100 \AA. The
velocity-resolved delays show consistent results: lags of $\sim$30--50 days at
the core of the broad H$\beta$ line and roughly zero lags at the wings.
H$\beta_{\rm IC}$ has a redshift of $\sim$400 $\rm km~s^{-1}$ which seems to be
stable for nearly 30 years by comparing with archived spectra, and may
originate from an infall. The root mean square (rms) spectrum of H$\beta_{\rm
VBC}$ shows a double-peaked profile with brighter blue peak and extended red
wing in the first year, which matches the signature of a thin disk. Both the
double-peaked profile and the near-zero lag suggest that H$\beta_{\rm VBC}$
comes from a region associated with the part of the accretion disc that emits
the optical continuum. Adopting the FWHM (in the rms spectrum) and the time lag
measured for the total H$\beta$ line, and a virial factor of 1.5, we obtain a
virial mass of $2.89_{-0.69}^{+0.60} \times10^7 M_{\odot}$ for the central
black hole in this quasar.
