2020ApJ...905...75H

We report on the results of a new spectroscopic monitoring campaign of the quasar PG 0026+129 at the Calar Alto Observatory 2.2 m telescope from 2017 July to 2020 February. Significant variations in the fluxes of the continuum and broad emission lines, including Hβ and He II, were observed in the first and third years, and clear time lags between them are measured. The broad Hβ line profile consists of two Gaussian components: an intermediate-width Hβ_IC with an FWHM of 1964 ± 18 kms^–1 and another very broad Hβ_VBC with an FWHM of 7570 ± 83 kms^–1. Hβ_IC has long time lags of ∼40-60 days in the rest frame, while Hβ_VBC shows nearly zero time delay with respect to the optical continuum at 5100 Å. The velocity-resolved delays show consistent results: lags of ∼30-50 days at the core of the broad Hβ line and roughly zero lags at the wings. Hβ_IC has a redshift of ∼400 kms^–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 Hβ_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 Hβ_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 Hβ line, and a virial factor of 1.5, we obtain a virial mass of 2.89_–0.69^+0.60×10⁷M_☉ for the central black hole in this quasar.