Continuum Variability of Active Galactic Nuclei in the Optical–Ultraviolet Range
Dario TreveseDipartimento di Fisica, Università di Roma “La Sapienza,” Piazzale A. Moro 2, I-00185 Roma, ItalyRichard G. KronFermi National Laboratory, MS 127, Box 500, Batavia, IL 60510Alessandro BunoneDipartimento di Fisica, Università di Roma “La Sapienza,” Piazzale A. Moro 2, I-00185 Roma, Italy
2001en
ABI
Abstract
The variability of the continuum spectral energy distribution has been analyzed for a complete magnitude-limited sample of quasars in Selected Area 57, observed at two epochs in the photographic U, BJ, F, and N bands with the Mayall 4 m telescope at Kitt Peak National Observatory. Changes δα of the spectral slope α appear correlated with brightness variations δ log fν, indicating an average hardening of the spectrum in the bright phases. This confirms that the correlation of variability with redshift, found in a single observing band, is due to intrinsic spectral changes. The average observed δα-δ log fν relation is consistent with the spectral change due to temperature variation of a blackbody of about 2.5 × 104 K.
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