Search for Sequential Variabilities in AGN Continua

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Session 34 -- Spectroscopy of AGN II: Broad Lines and Spectral Evolution
Oral presentation, Monday, 9, 1995, 2:00pm - 3:30pm

[34.05] Search for Sequential Variabilities in AGN Continua

W.-H. Sun (National Central University), T.-C. Lin (National Central University), C.-H. Chen (National Central University), M.A. Malkan (UCLA), R.P.S. Stone (Lick Observatory)

The observed strong UV/Optical excess in many Seyfert 1 active galactic nuclei (AGNs) and quasars (QSOs) is well described as thermal radiation from the surface of an optically thick accretion disk surrounding a supermassive black hole. This scenario naturally leads to a radially symmetric temperature gradient with the innermost regions the hottest. Thus for a perturbation generated in the inner regions propagating outward, sequential variations from higher to lower frequencies should be expected, aside from the bolometric increase of brightness.

We have launched a one-year monitoring program, approximately once every month, starting June 1994, on a sample of 8 Seyfert~1 galaxies with CCD direct imaging and differential photometry on the 1.0m telescope at Lick Observory to search for more conclusive evidence on these sequential variabilities which may provide stringent constraint on accretion disk or other continuum models. We measured the variabilities of the target AGNs at $3890$\AA~(U), $5750$\AA~(V), $8020$\AA (I), and $9750$\AA (Z), with two-inch square intermediate band filters developed in the BATC project. Preliminary data analysis shows an observational accuracy of 1\% or better for some AGNs with adequate comparison stars. Details of observing strategy and preliminary results will be discussed.

Monday program listing