PMN J0525-3343: Soft X-ray spectral flattening in a blazar at z = 4.4

A. C. Fabian, A. Celotti, K. Iwasawa, R. G. McMahon, C. L. Carilli, W. N. Brandt, G. Ghisellini, I. M. Hook

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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 RXJ1028.6-0844 (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.

Original languageEnglish (US)
Pages (from-to)373-379
Number of pages7
JournalMonthly Notices of the Royal Astronomical Society
Volume323
Issue number2
DOIs
StatePublished - May 11 2001

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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