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Session 16 - QSOs and Active Galaxies.
Oral session, Monday, June 08

[16.07] NGC 3516: Variability of the AGN Absorption and Emission Line Regions

A. Koratkar, M. Goad, J. Kim (STScI), P. T. O'Brien (U. Leicester), K. T. Korista (Dept. of Physics, Western Michigan U.), D. J. Axon (Nuffield Radio Astronomy Lab., U. Manchester)

NGC 3516 displays the strongest intrinsic, blue-shifted UV absorption lines of any Seyfert 1 galaxy. We report on UV spectrophotometric monitoring data obtained over a period of 11 months using the HST/FOS.

During the (HST/FOS) observation period, the UV continuum showed a factor of 5 variation, spanning almost the entire range in continuum flux seen in over 15 years of IUE/SWP data. The high ionization emission lines of \mbox Ly\alpha \lambda 1215, \mbox C\,\sc iv \lambda 1549, \mbox N\,\sc v \lambda 1240, and \mbox He\,\sc ii \lambda 1640 showed significant variation (a factor of \sim2), while the low ionization lines of \mbox Mg\,\sc ii \lambda 2798 and \mbox Fe\,\sc ii showed no significant variation (<7%) within the signal-to-noise of our data.

Our spectra clearly show narrow (FWHM\sim 200--500 km s^-1) intrinsic absorption lines of highly ionized species (eg, \mbox Ly\alpha \lambda 1215, \mbox N\,\sc v \lambda 1240, \mbox Si\,\sc iv \lambda 1397, and \mbox C\,\sc iv \lambda 1549). We also note that we do not observe the higher velocity \mbox C\,\sc iv absorption-line component seen in the historic IUE/SWP spectra. There is no firm evidence for a variable narrow absorption line component in these data over the course of our observing campaign (\sim 11 months) indicating that the narrow absorption line region remains stable on timescales of at least one year. Yet, a comparison of these HST/FOS spectra with archival HST/GHRS spectra demonstrates that there has been a clear change in the physical condtions of the absorption line gas prior to the onset of our observing campaign.

We have also investigated the line profile variability in this object and investigate the kinematic structure of the Broad Line Region in NGC 3516.

Program listing for Monday