2019ApJ...876...49Z

Despite many decades of study, the kinematics of the broad-line region of 3C 273 are still poorly understood. We report a new, high signal-to-noise, reverberation mapping campaign carried out from 2008 November to 2018 March that allows the determination of time lags between emission lines and the variable continuum with high precision. The time lag of variations in Hβ relative to those of the 5100 Å continuum is 146.8_–12.1^+8.3 days in the rest frame, which agrees very well with the Paschen-α region measured by the GRAVITY at The Very Large Telescope Interferometer. The time lag of the Hγ emission line is found to be nearly the same as that for Hβ. The lag of the Fe II emission is 322.0_–57.9^+55.5 days, longer by a factor of ∼2 than that of the Balmer lines. The velocity-resolved lag measurements of the Hβ line show a complex structure that can be possibly explained by a rotation-dominated disk with some inflowing radial velocity in the Hβ-emitting region. Taking the virial factor of f_BLR = 1.3, we derive a BH mass of M_•=4.1_–0.4^+0.3×10⁸M_☉ and an accretion rate of 9.3L_Eddc^–2 from the Hβ line. The decomposition of its Hubble Space Telescope images yields a host stellar mass of M_*=10^11.3±0.7^M_☉, and a ratio of M_•/M_*~2.0×10^–3 in agreement with the Magorrian relation. In the near future, it is expected to compare the geometrically thick BLR discovered by the GRAVITY in 3C 273 with its spatially resolved torus in order to understand the potential connection between the BLR and the torus.