Bloated stars as AGN broad-line clouds: the emission-line response to continuum variations

The `Bloated Stars Scenario' proposes that AGN broad line emission originatesin the winds or envelopes of bloated stars (BS). Alexander and Netzer (1994,1996) established that ~ 5e4 BSs with dense, decelerating winds can reproducethe observed emission line spectrum and line profiles while avoiding rapidcollisional destruction. Here, I investigate a third prediction of the model,related to the size of the broad line region, by deriving the emission lineresponse to variations in the ionizing continuum (`line reverberation') andcomparing it to observations. The expected time lags, as well as the order ofresponse of the various lines, strongly depend on the typical variability timescale of the ionizing continuum. The BS model studied here corresponds to abright Syfert 1 galaxy (Sy1) or a low luminosity QSO. I find that the BS modelis consistent with the observed correlation between the Balmer lines time lagsand the AGN luminosity, which at present is the only line reverberationinformation available for this luminosity class. The model displays also someof the anti-correlation between the time lags of the metal emission lines andtheir degree of ionization that has been observed in a few low-luminosity Sy1s.However, the bright Sy1 model results differs from the low-luminosity Sy1 datain that the Hb time lag is relatively shorter and the CIV time lag relativelylonger.Comment: 6 pages with 4 figures, LaTeX using mn.sty and epsf.sty, to appear in MNRA