2011MNRAS.418...90L

In this paper, a new method is proposed to estimate the broad-line region sizes of ultraviolet (UV) lines R^uv_BLR. It is applied to 3C 273. First, we derive the time lags of radio emission relative to broad emission lines Lyα and C IV by the z-transformed discrete correlation function (ZDCF) method. The broad lines lag the 5-, 8-, 15-, 22- and 37-GHz emission. The measured lags τ^uv_ob are of the order of years. For a given line, τ^uv_ob decreases as the radio frequency increases. This trend results from the radiative cooling of relativistic electrons. Both UV lines have a lag of τ^uv_ob=-2.74^+0.06_- 0.25_ yr relative to the 37-GHz emission. These results are consistent with those derived from the Balmer lines in Paper I. Secondly, we derive the time lags of the lines Lyα, C IV, Hγ, Hβ and Hα relative to the 37-GHz emission by the flux randomization/random subset selection (FR/RSS) Monte Carlo method. The measured lags are τ_ob=-3.40^+0.31_- 0.05_, -3.40^+0.41_- 0.14_, -2.06^+0.36_- 0.92_, -3.40^+1.15_- 0.20_ and -3.56^+0.35_- 0.18_yr for the lines Lyα, C IV, Hγ, Hβ and Hα, respectively. These estimated lags are consistent with those derived by the ZDCF method within the uncertainties. Based on the new method, we derive R^uv_BLR= 2.54^+0.71_- 0.35_ to 4.01^+0.90_- 1.16_and 2.54^+0.80_- 0.43_to 4.01^+0.98_- 1.24_light-years for the Lyα and C IV lines, respectively. Considering the uncertainties, these estimated sizes are consistent with those obtained in the classical reverberation mapping for the UV and the Balmer lines. This indicates that their emitting regions are not separated so large as in the classical mapping of the UV and optical lines. These results seem to depart from the stratified ionization structures obtained in the classical mapping.