2021ApJ...911...64W

We present the first results of a 4.5 yr monitoring campaign of the three bright images of multiply imaged z = 2.805 quasar SDSS J2222+2745 using the Gemini North Multi-Object Spectrograph and the Nordic Optical Telescope. We take advantage of gravitational time delays to construct light curves surpassing 6 yr in duration in the observed frame and achieve an average spectroscopic cadence of 10 days during the 8 months of visibility per season. Using multiple secondary calibrators and advanced reduction techniques, we achieve percent-level spectrophotometric precision and carry out an unprecedented reverberation mapping analysis, measuring both integrated and velocity-resolved time lags for the C IV emission line. The full line lags the continuum by τ_cen=36.5_–3.9^+2.9 rest-frame days. We combine our measurement with published C IV emission line lags and derive the r_BLR - L relationship log₁₀(τ/day)=(0.99±0.07)+(0.48±0.03)log₁₀[λL_λ(1350AA)/10⁴⁴ergs^–1] with 0.30 ± 0.06 dex intrinsic scatter. The velocity-resolved lags are consistent with circular Keplerian orbits, with τ_cen=86.2_–5.0^+4.5, 25_–15⁺¹¹, and 7.5_–3.5^+4.2 rest-frame days for the core, blue wing, and red wing, respectively. Using σ_line with the mean spectrum and assuming log₁₀(f_mean,σ)=0.52±0.26, we derive log₁₀(M_BH/M_☉)=8.63±0.27. Given the quality of the data, this system represents a unique benchmark for calibration of M_BH estimators at high redshift. Future work will present dynamical modeling of the data to constrain the virial factor f and M_BH.