1997A&A...318..331D

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 (P≫99%) 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.