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.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science