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Astron. Astrophys. 318, 331-336 (1997)

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Rapid infrared spectral variability of 3C 66A in outburst

J.A. De Diego * 1, M.R. Kidger 1, J.N. Gonzáles-Pérez 1 and Harry J. Lehto 2

1 Instituto de Astrofísica de Canarias, C/Via Lactea, s/n, E-38200 La Laguna, Tenerife, Spain
2 Tuorla Observatory, Tuorla, SF-21500 Piikkiö, Finland

Received 17 February 1995 / Accepted 17 June 1995


Infrared observations taken during the major outburst seen in 1993 show strong evidence of rapid variability in 3C 66A on a time scale of a few hours, with associated variability of the spectral slope on the same time scale. A strong ([FORMULA]) correlation is seen between the flux at 2.2 microns and the spectral index, with the spectrum steepening as the flux rises, the opposite trend to that seen normally in blazars. Such rapid variability cannot easily be explained by current relativistic jet models; a better option is black body radiation from hot spots on the accretion disk, possibly linked to strong magnetic fields, although the rapid time scale of the variation and its energetics pose serious problems. One possible solution is to invoke bremsstrahlung radiation from a flare, which is later modified by a high degree of extinction through the disk.

Key words: quasars: 3C 66A – infrared: galaxies – accretion, accretion disks – radiation mechanisms: thermal – radiation mechanisms: non-thermal

* Now at Instituto de Astronomía, Universidad Nacional Autonoma de México, Apartado Postal 70-256, México D.F., 04510 Mexico

Send offprint requests to: M.R. Kidger

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© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998