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

TL;DR

This study extends reverberation mapping of quasar PG 2130+099 over four years, revealing a doubling of the broad-line region size and complex dynamics, challenging previous inconsistent measurements and suggesting geometric dilution effects.

Contribution

It provides the first long-term, high-cadence monitoring of PG 2130+099, demonstrating significant BLR size variation and complex velocity-resolved delays, advancing understanding of quasar BLR dynamics.

Findings

Hβ lag increased by a factor of two in two years

Velocity delays show virial motion and inflow signs

Significant scatter in R-L relationship due to size changes

Abstract

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'.