Evidence for Two Distinct Broad-Line Regions from Reverberation Mapping of PG 0026+129

Abstract

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${\beta }_{\mathrm{IC}}$ with a full width at half-maximum (FWHM) of 1964$\pm$18 $\mathrm{km}{\mathrm{s}}^{-1}$ and another very broad H${\beta }_{\mathrm{VBC}}$ with a FWHM of 7570$\pm$83 $\mathrm{km}{\mathrm{s}}^{-1}$. H${\beta }_{\mathrm{IC}}$ has long time lags of $\sim$40--60 days in the rest frame, while H${\beta }_{\mathrm{VBC}}$ shows nearly zero time delay with respect to the optical continuum at 5100 Å. 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${\beta }_{\mathrm{IC}}$ has a redshift of $\sim$400 $\mathrm{km}{\mathrm{s}}^{-1}$ 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${\beta }_{\mathrm{VBC}}$ 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${\beta }_{\mathrm{VBC}}$ 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 $2.89_{-0.69}^{+0.60}\times 10^7{M}_{\odot }$ for the central black hole in this quasar.

21 pages, 17 figures, accepted for publication in The Astrophysical Journal

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