南方基地知识库

We restudy the issue of cross-correlations between broad-line and jet emission variations, and aim to locate the position of a radio (and gamma-ray) emitting region in a jet of active galactic nuclei. Considering the radial profiles of the radius and number density of clouds in a spherical broad-line region (BLR), we derive new formulae connecting the jet-emitting position R-jet to the time lag tau(ob) between broad-line and jet emission variations, and the BLR radius. Also, formulae are derived for a disc-like BLR and a spherical shell BLR. The model-independent flux randomization/random subset selection method is used to estimate tau(ob). For 3C 120, positive lags of about 0.3 yr are found between the 15 GHz emission and the H beta, H gamma and He II lambda 686 lines, including broad-line data in a newly published paper, indicating that the line variations lead the 15 GHz ones. Each of the broad-line light curves corresponds to a radio outburst. R-jet = 1.1-1.5 parsec (pc) is obtained for 3C 120. For 3C 273, a common feature of negative time lags is found in the cross-correlation functions between light curves of radio emission and the Balmer lines, as well as Ly alpha lambda 1216 and CIV lambda 1549 lines. R-jet = 1.0-2.6 pc is obtained for 3C 273. The estimated R-jet is comparable for 3C 120 and 3C 273, and the gamma-ray-emitting positions will be within similar to 1-3 pc from the central engines. Comparisons show that the cloud number density and radius radial distributions and the BLR structures have only negligible effects on R-jet.