X-ray and UV observations of the BL Lacertae object 3C 66A.

Abstract

The energy distribution of the BL Lac object 3C 66A has been investigated in the soft X-ray range by means of repeated observations with the Einstein Observatory and in the UV range by means of the IUE satellite. The available optical photometry from 1979 to 1981 is reported. 3C 66A is characterized by violent X-ray activity over a time scale of 6 months, probably uncorrelated with optical variations. The featureless UV continuum is steeper than that deduced from infrared broad-band photometry, thus indicating a spectral break in the region 10 to the 14th - 10 to the 15th Hz. The overall energy distribution is discussed in the framework of theoretical models proposed for BL Lac objects. The spectral properties indicate that synchrotron radiation is the dominant mechanism at all wavelengths, while the different optical and X-ray variability suggests different emission regions.