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Far UV observations of PKS2155-304

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 ≲ 10 4 K) 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 Ly α , whi...

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Bibliographic Details
Published in:Nature (London) 1980-06, Vol.285 (5766), p.555-557
Main Authors: Maraschi, L, Tanzi, E. G, Tarenghi, M, Treves, A
Format: Article
Language:English
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Summary: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 ≲ 10 4 K) 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 Ly α , 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 10 15 Hz.
ISSN:0028-0836
1476-4687
DOI:10.1038/285555a0