Astronomy and Astrophysics – Astrophysics
Scientific paper
2000-11-30
Mon.Not.Roy.Astron.Soc.323:373,2001
Astronomy and Astrophysics
Astrophysics
7 pages, 7 figures; MNRAS, in press
Scientific paper
10.1046/j.1365-8711.2001.04181.x
We report optical, radio and X-ray observations of a new distant blazar, PMN J0525-3343, at a redshift of 4.4. The X-ray spectrum measured from ASCA and BeppoSAX flattens below a few keV, in a manner similar to the spectra of two other z>4 blazars, GB 1428+4217 (z=4.72) reported by Boller et al and RXJ 1028.6-0844 (z=4.28) by Yuan et al. The spectrum is well fitted by a power-law continuum which is either absorbed or breaks at a few keV. An intrinsic column density corresponding to 2 x 10^23 H-atoms cm-2 at solar abundance is required by the absorption model. This is however a million times greater than the neutral hydrogen, or dust, column density implied by the optical spectrum, which covers the rest-frame UV emission of the blazar nucleus. We discuss the problems raised and suggest that, unless there is intrinsic flattening in the spectral distribution of the particles/seed photons producing X-rays via inverse Compton scattering, the most plausible solution is a warm absorber close to the active nucleus.
Brandt Wiliam N.
Carilli Chris L.
Celotti Annalisa
Fabian Andrea C.
Ghisellini Gabriele
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