The following document lists the file abstract/ATREVES_PKS_SPEC.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
We propose to observe the prototype X-ray bright BL Lac object PKS 2155-304 with ISO in order to accurately measure its spectrum in the 2-200 micron range. Both ISOPHOT and ISOCAM will be used in order to achieve the best spectral coverage in the full band. From previous studies of the radio and IR- optical emission it is inferred that the dominant mechanism is synchrotron radiation. By spectral continuity and time correlation arguments, in this object synchrotron radiation appears to extend to the X-ray band. A connection of the UV-optical near IR continuum with the flat spectrum radio component requires a steepening by about 0.5 in spectral index. The proposed observations will allow to measure a spectral change of this order within the ISO range or constrain the change to fall outside the wide explored band. In particular the observations could reveal the presence of a selfabsorption feature at 30 micron anticipated by some models, with important consequences for estimates of the physical parameters of the emission region. Multifrequency observations from the near infrared to the X-ray band (in which the team has been involved for many years) will be attempted in order to maximise the scientific value of the ISO observations. This proposal is complementary to the one for a time variability study of the same object in selected wavelength intervals (GTAGLIAF.PKS_VARI). Since PKS 2155-304 is representative of the class of X-ray bright BL Lacs, a detailed spectral study of this object in the ISO band is crucial to understand the difference in spectral energy distributions of X-ray bright and radio bright BL Lacs. Should the ISO observations give evidence that the flat radio to IR spectrum of PKS 2155-304 is due to high frequency self absorption, an emission region with small size and high magnetic field would be indicated, which may represent a physical distinction with respect to the (expected) thin synchrotron emission in the ISO band from radio-bright BL Lac objects.