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 2017 July to 2020 February. 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(IC) with an FWHM of 1964 +/- 18 km s(-1) and another very broad H beta(VBC) with an FWHM of 7570 +/- 83 km s(-1). H beta(IC) has long time lags of similar to 40-60 days in the rest frame, while H beta(VBC) shows nearly zero time delay with respect to the optical continuum at 5100 A. The velocity-resolved delays show consistent results: lags of similar to 30-50 days at the core of the broad H beta line and roughly zero lags at the wings. H beta(IC) has a redshift of similar to 400 km s(-1), which seems to be stable for nearly 30 yr by comparing with archived spectra, and may originate from an infall. The rms spectrum of H beta(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(VBC) comes from a region associated with the part of the accretion disk 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) x 10(7) M-circle dot for the central black hole in this quasar.