Astronomy and Astrophysics – Astrophysics
Scientific paper
2001-01-17
Mon.Not.Roy.Astron.Soc.324:628,2001
Astronomy and Astrophysics
Astrophysics
7 pages, 13 figures; MNRAS, in press
Scientific paper
10.1046/j.1365-8711.2001.04348.x
BeppoSAX 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 ~ 8 x 10^22 cm^-2. Below 2 keV a (variable) excess of a factor ~ 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 ~ 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 ~ 300 keV (rest frame).
Celotti Annalisa
Fabian Andrea C.
Ghisellini Gabriele
Iwasawa Kashuzi
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