Optical spectral variability of quasars and BL Lac Objects is compared by means of the spectral variability parameter beta (Trevese & Vagnetti 2002). Both kinds of objects change their spectral slopes alpha, becoming bluer when brighter, but BL Lac Objects have smaller beta values and are clearly separated from quasars in the alpha-beta plane. Models accounting for the origin of the variability are discussed for both classes of objects.
Cite
@article{arxiv.astro-ph/0212474,
title = {Color Variability of AGNs},
author = {F. Vagnetti and D. Trevese},
journal= {arXiv preprint arXiv:astro-ph/0212474},
year = {2007}
}
Comments
4 pages, 1 figure, Mem. SAIt LaTeX class mem.cls, to appear in "Workshop on Variability with Wide Field Imagers", Lampedusa, Italy, September 2002