Abstract
In BL Lac objects the absence of broad emission lines may be due either to a lack of ionizing continuum or to a lack of cool gas (T ≲ 104K)1. UV observations of BL Lac objects are interesting in that they provide a measurement of the continuum, and they include the wavelength range of Lyα, which is in principle the most favourable line for detection. We report here several spectra of the BL Lac object PKS2155–304 in the 1,150–3,200 A band taken with the IUE when the object was in a bright phase. The UV flux connects smoothly with the optical and IR observations of the source in its brightest state and its extrapolation matches the soft X-ray flux, implying a change in spectral slope around 1015Hz.
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Maraschi, L., Tanzi, E., Tarenghi, M. et al. Far UV observations of PKS2155–304. Nature 285, 555–557 (1980). https://doi.org/10.1038/285555a0
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DOI: https://doi.org/10.1038/285555a0
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