Beppo SAX observations of the high redshift ( z = 4.72 ) blazar GB 1428+4217 confirm the presence of a complex soft X–ray spectrum first seen with the ROSAT PSPC .
Flattening below a rest frame energy of 5 keV can be accounted for by absorption from an equivalent column density of ( cold ) gas with N _ { H } \sim 8 \times 10 ^ { 22 } cm ^ { -2 } .
Below 2 keV a ( variable ) excess of a factor \sim 20 above the extrapolated absorbed spectrum is also detected .
These findings are consistent with and extend to higher redshifts the correlation between increasing soft X–ray flattening and increasing z , previously pointed out for large samples of radio–loud quasars .
We propose that such features , including X–ray absorption , soft excess emission as well as absorption in the optical spectra , can be satisfactorily accounted for by the presence of a highly–ionized nuclear absorber with column N _ { H } \sim 10 ^ { 23 } cm ^ { -2 } , with properties possibly related to the conditions in the nuclear regions of the host galaxy .
High energy X–ray emission consistent with the extrapolation of the medium energy spectrum is detected up to \sim 300 keV ( rest frame ) .