The blazar GB 1428+4217: a warm absorber at z=4.72? |
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| Authors: | AC Fabian A Celotti K Iwasawa G Ghisellini |
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| Institution: | ;1Institute of Astronomy, Madingley Road, Cambridge CB3 0HA;2SISSA, via Beirut, 2-4, 34014 Trieste, Italy;3Osservatorio Astronomico di Brera-Merate, via Bianchi 46, 23807 Merate (LC), Italy |
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| Abstract: | 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∼8×1022 cm−2 . Below 2 keV a (variable) excess of a factor of ∼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 and 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∼1023 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). |
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| Keywords: | galaxies: active galaxies: individual: GB 1428+4217 X-rays: galaxies |
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