Constraining broad-line regions from time lags of broad emission lines
  relative to radio emission
  In this paper, a new method is proposed to estimate the broad-line region
sizes of UV lines $R^{\rm{uv}}_{\rm{BLR}}$. It is applied to 3C 273. First, we
derive the time lags of radio emission relative to broad emission lines
Ly$\alpha$ and C IV by the ZDCF method. The broad lines lag the 5, 8, 15, 22
and 37 GHz emission. The measured lags $\tau^{\rm{uv}}_{\rm{ob}}$ are of the
order of years. For a given line, $\tau^{\rm{uv}}_{\rm{ob}}$ decreases as the
radio frequency increases. This trend results from the radiative cooling of
relativistic electrons. Both UV lines have a lag of
$\tau^{\rm{uv}}_{\rm{ob}}=-2.74^{+0.06}_{-0.25}$ yr relative to the 37 GHz
emission. These results are consistent with those derived from the Balmer lines
in Paper I. Second, we derive the time lags of the lines Ly$\alpha$, CIV,
H$\gamma$, H$\beta$ and H$\alpha$ relative to the 37 GHz emission by the FR/RSS
Monte Carlo method. The measured lags are
$\tau_{\rm{ob}}=-3.40^{+0.31}_{-0.05}$, $-3.40^{+0.41}_{-0.14}$,
$-2.06^{+0.36}_{-0.92}$, $-3.40^{+1.15}_{-0.20}$ and $-3.56^{+0.35}_{-0.18}$ yr
for the lines Ly$\alpha$, CIV, H$\gamma$, H$\beta$ and H$\alpha$, respectively.
These estimated lags are consistent with those derived by the ZDCF method
within the uncertainties. Based on the new method, we derive
$R^{\rm{uv}}_{\rm{BLR}}=2.54^{+0.71}_{-0.35}$--$4.01^{+0.90}_{-1.16}$ and
$2.54^{+0.80}_{-0.43}$--$4.01^{+0.98}_{-1.24}$ light-years for the Ly$\alpha$
and CIV lines, respectively. Considering the uncertainties, these estimated
sizes are consistent with those obtained in the classical reverberation mapping
for the UV lines 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.
