Open AccessPMN J0525−3343: soft X‐ray spectral flattening in a blazar at z = 4.4
Author(s) -
Fabian A. C.,
Celotti A.,
Iwasawa K.,
McMahon R. G.,
Carilli C. L.,
Brandt W. N.,
Ghisellini G.,
Hook I. M.
Publication year - 2001
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2001.04181.x
Subject(s) - physics , blazar , astrophysics , flattening , redshift , quasar , spectral line , photon , compton scattering , rest frame , active galactic nucleus , ultraviolet , gamma ray , astronomy , galaxy , optics
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 2×10 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 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.