1998A&A...333L...5G

A long (>100,000 seconds) observation of the bright BL Lac object PKS 2155-304 has been carried out with the Narrow Field Instruments of the BeppoSAX satellite as part of the Science Verification Phase. The source was detected between 0.1 and about 100keV at an intermediate intensity level compared to previous observations. The unique spectral coverage of BeppoSAX has allowed us to detect a number of spectral features. Between 0.1 and 10keV the spectrum can be well described by a convex spectrum with (energy) slope gradually steepening from 1.1 to 1.6. At higher energies evidence for a sharp spectral hardening is found, while in the soft X-rays (0.1-1.0keV) some evidence for an absorption feature was found. Indication for an emission line at 6.4keV in the source rest frame is present. Repeated variability of ≃20-30% around the mean flux is clearly detected on time scales of a few hours. From the symmetry and timescale of the observed variations we derive limits on the magnetic field and on the maximum energy of the emitting particles, implying that PKS 2155-304 should not be bright at TeV energies.