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Astron. Astrophys. 348, 63-70 (1999)

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8. Summary and conclusions

From the analysis of the Beppo SAX and ASCA data, and from the construction of the simultaneous SED of the source at different epochs we find:

  • Beppo SAX observed PKS 0528+134 in its faintest X-ray state, characterized by the flattest X-ray spectrum, of energy index [FORMULA].

  • The three ASCA observations of March 1995, despite the different fluxes, are characterized by the same spectral index [FORMULA]. Fitting the sum of these data allows to determine with improved precision the absorbing hydrogen column density of the source, [FORMULA] cm-2, which corresponds to an optical absorption of [FORMULA].

  • The overall simultaneous SED follows the general trend of blazars, as found by Fossati et al. (1998). In fact the SED is characterized by two peaks, in the mid or far infrared and in the MeV band, respectively, as for the most luminous blazars. Furthermore the [FORMULA]-ray luminosity dominates the overall power output during active states, again in agreement with the general behavior of other powerful blazars (see e.g. von Montigny et al., 1995).

  • We have fitted the 1995 SED (high state) and the 1997 SED (low state) with a homogeneous model, in which the emission from the far IR to the UV is produced by the synchrotron process, and the high energy flux is due to the sum of the synchrotron self-Compton and the external Compton contributions. The former becomes more important (in the X-ray band) for increasing source power. This accounts for the unusual observed X-ray behavior (flatter state when the source was fainter). Variations of the [FORMULA]-ray flux and spectral shape might be explained by a flattening of the high energy part of the electron distribution.

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© European Southern Observatory (ESO) 1999

Online publication: July 16, 1999