X-ray absorption toward the red quasar 3C 212

Abstract

A Roentgen Satellite (ROSAT) X-ray spectrum of the z = 1.049 'red quasar' 3C 212 has a strong low-energy cutoff. The spectrum can be fitted with a power law (of energy index 1.4(+0.8, -0.6) with low-energy photoelectric absorption in excess of the Galactic value that, if at the redhsift of the quasar, would have a column density of (0.9(+0.8, -0.6)) x 1022 atoms/sq cm. Possible sites for the absorption are a nuclear torus, an intervening damped Lyman-alpha system, or intracluster material (e.g., a cooling flow) around the quasar. The implied absorbing column density is sufficient to redden a normal quasar spectrum to the observed steep optical slope. The observed continuum, if dereddened by this amount, can produce the observed emission line fluxes and ratios. The absence of the graphite lambda-2175 feature in 3C 212 however, requires dust different from the local Milky Way composition, or an intervening absorber with z less than 0.4. Alternative acceptable fits to the X-ray spectrum are (1) a blackbody with a temperature of 0.7 keV (in the quasar frame) modified only by Galactic absorption, and (2) an optically thin thermal plasma with excess absorption. Although a blackbody spectrum would be unprecedented, the model is consistent with all the available X-ray and optical data and cannot be ruled out. We discuss possible observations that can discriminate among the above models.