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3.6. AGN variability studies: an agenda for the next millenium?

Published online by Cambridge University Press:  25 May 2016

M.-H. Ulrich
M.-H. Ulrich*
Affiliation:
European Southern Observatory, Karl-Schwarzschild Str. 2, 85748 Garching, Germany

Extract

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Data which are obtained today can be re-acquired better and faster in the future. Their only enduring value, after they have been interpreted, is as historical markers. With electronic archiving one can envision archives covering decades, centuries and even longer periods of observations of selected objects or classes of objects. Such a data base would allow the study of phenomena with low temporal frequencies, and of rare events.

First hints of such phenomena in AGN have been discovered recently: 1) The Seyfert 1s, the best studied AGN at present, exhibit flux variations on time scales ranging from hours to several years (see Ulrich et al. 1997). The faster variations (up to months) have been extensively observed, and they are best understood as being caused by magnetic flares in the corona above the central part of the accretion disk (Blandford and Payne 1982). The origin of the long term and large amplitude UV/optical flux variations (factor 20 in several years as observed in NGC4151 and F9), however, remain essentially unknown.

Type
Part I. Stellar Cluster, Star Formation
Information
Symposium - International Astronomical Union , Volume 184: The Central Regions of the Galaxy and Galaxies , 1998 , pp. 99 - 101
Copyright
Copyright © Kluwer 1998 

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