Revisiting correlations between broad-line and jet emission variations for AGNs: 3C 120 and 3C 273

Abstract

We restudy the issue of cross-correlations between broad-line and jet emission variations, and aim to locate the position of radio (and gamma-ray) emitting region in jet of active galactic nuclei (AGNs). Considering the radial profiles of the radius and number density of clouds in a spherical broad-line region (BLR), we derive new formulae connecting jet emitting position R jet to time lag τ ob between broad-line and jet emission variations, and BLR radius. Also, formulae are derived for a disk-like BLR and a spherical shell BLR. The model-independent FR/RSS method is used to estimate τ ob . For 3C 120, positive lags of about 0.3 yr are found between the 15 GHz emission and the Hβ, Hγ and He II λ4686 lines, including broad-line data in a newly published paper, indicating 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) are 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, and as well Lyα λ1216 and C iv λ1549 lines. R jet = 1.0-2.6 pc are obtained for 3C 273. The estimated R jet are comparable for 3C 120 and 3C 273, and the gamma-ray emitting positions will be within ∼ 1-3 pc from the central engines.Comparisons show that the cloud number density and radius radial distributions and the BLR structures only have negligible effects on R jet .

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“…• 3C 120 (z = 0.033) [209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,224,225,226,227,228,229,230];…”

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