Measurement of the Broad-Line Region Size in Two Bright Quasars

We present 4 years of spectrophotometric monitoring data for two radio-quiet quasars, PG 0804+762 and PG 0953+414, with typical sampling intervals of several months. Both sources show continuum and emission-line variations. The variations of the Hβ line follow those of the continuum with a time lag, as derived from a cross-correlation analysis, of 93 ± 30 days for PG 0804+762 and 111 ± 55 days for PG 0953+414. This is the first reliable measurement of such a lag in active galactic nuclei with luminosity L > 1045 ergs s-1. The broad-line region (BLR) size that is implied is almost an order of magnitude larger than that measured in several Seyfert 1 galaxies and is consistent with the hypothesis that the BLR size grows as L0.5.

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