Quasi-simultaneous ultraviolet and optical observations of PKS 2155-304 = H 2155-304.
Maraschi, L.; Tanzi, E. G.; Tarenghi, M.; Treves, A.
Italy, Germany
Abstract
The BL Lac object PKS 2155-304 was repeatedly observed in the 1200-3000 Å band with the International Ultraviolet Explorer. The variability of the source in this band is studied in detail. The UV continua are well fitted by power laws with frequency spectral index αν varying between -0.7 and -0.9. An optical spectrum was taken within one day from a UV spectrum. Combining the observations in the two ranges, evidence is found of a spectral steepening by Δαν = 0.36 around 1015 Hz.