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PMN J0525−3343: soft X-ray spectral flattening in a blazar at z = 4.4
Authors:A C Fabian  A Celotti  K Iwasawa  R G McMahon  C L Carilli  W N Brandt  G Ghisellini  I M Hook
Institution:Institute of Astronomy, Cambridge University, Madingley Road, Cambridge CB3 0HA;S. I. S. S. A., via Beirut 2-4, I-34014 Trieste, Italy;NRAO, P O Box 0, Socorro, NM 87801, USA;Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA;Osservatorio Astronomico di Brera-Merate, via Bianchi 46, I-23807 Merate (LC), Italy;Institute for Astronomy, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ
Abstract: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 RX J1028.6−0844 ( z =4.28) reported by Yuan et al. The spectrum is well fitted by a power-law continuum which either is absorbed or breaks at a few keV. An intrinsic column density corresponding to 2×1023 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 ultraviolet 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.
Keywords:galaxies: active  galaxies: individual: PMN J0525−3343  X-rays: galaxies
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