Broad-line Region of the Quasar PG 2130+099. II. Doubling the Size Over Four Years?

Zhu-Heng Yao, Sen Yang, Wei-Jian Guo, Yong-Jie Chen, Yu-Yang Songsheng, Dong-Wei Bao, Bo-Wei Jiang, Yi-Lin Wang, Hao Zhang, Chen Hu, Yan-Rong Li, Pu Du, Ming Xiao, Jin-Ming Bai, Luis C. Ho, Michael S. Brotherton, Jesús Aceituno, Hartmut Winkler, Jian-Min Wang

Published 2024-08-30Version 1

Over the past three decades, multiple reverberation mapping (RM) campaigns conducted for the quasar PG 2130+099 have exhibited inconsistent findings with time delays ranging from $\sim$10 to $\sim$200 days. To achieve a comprehensive understanding of the geometry and dynamics of the broad-line region (BLR) in PG 2130+099, we continued an ongoing high-cadence RM monitoring campaign using the Calar Alto Observatory 2.2m optical telescope for an extra four years from 2019 to 2022. We measured the time lags of several broad emission lines (including He II, He I, H$\beta$, and Fe II) with respect to the 5100 {\AA} continuum, and their time lags continuously vary through the years. Especially, the H$\beta$ time lags exhibited approximately a factor of two increase in the last two years. Additionally, the velocity-resolved time delays of the broad H$\beta$ emission line reveal a back-and-forth change between signs of virial motion and inflow in the BLR. The combination of negligible ($\sim$10%) continuum change and substantial time-lag variation (over two times) results in significant scatter in the intrinsic $R_{\rm H\beta}-L_{\rm 5100}$ relationship for PG 2130+099. Taking into account the consistent changes in the continuum variability time scale and the size of the BLR, we tentatively propose that the changes in the measurement of the BLR size may be affected by 'geometric dilution'.