NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-16 T00:53:46 PDT
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For refcode 2005A&A...443..451F:
Retrieve 15 NED objects in this reference.
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2005A&A...443..451F AGN variability time scales and the discrete-event model P. Favre, T. J.-L. Courvoisier and S. Paltani Received 25 August 2004 / Accepted 3 August 2005 We analyse the ultraviolet variability time scales in a sample of 15 type 1 Active Galactic Nuclei (AGN) observed by IUE. Using a structure function analysis, we demonstrate the existence in most objects of a maximum variability time scale of the order of 0.02-1.00 year. We do not find any significant dependence of these maximum variability time scales on the wavelength, but we observe a weak correlation with the average luminosity of the objects. We also observe in several objects the existence of long-term variability, which seems decoupled from the short-term one. We interpret the existence of a maximum variability time scale as a possible evidence that the light curves of type 1 AGN are the result of the superimposition of independent events. In the framework of the so-called discrete-event model, we study the event energy and event rate as a function of the object properties. We confront our results to predictions from existing models based on discrete events. We show that models based on a fixed event energy, like supernova explosions, can be ruled out. In their present form, models based on magnetic blobs are also unable to account for the observed relations. Stellar collision models, while not completely satisfactory, cannot be excluded. Key words: galaxies: active, galaxies: Seyfert, quasars: general, ultraviolet: galaxies
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