X-ray/optical brightness trends in 3C 66A.

Abstract

New X-ray and optical observations of the BL Lac object 3C 66A show small amplitude (≡30%) variability occurring probably contemporaneously in both ranges. The time scale is of the order of a week. This indicates that small intensity variations engage the whole electromagnetic spectrum of the source between visible and X-ray wavelengths, while large outbursts are mainly confined in the X-ray band. No evidence is found for a steep X-ray spectrum at times of low intensity levels, as had been previously found, hinting to a different physical process in the source at times of large X-ray outbursts.