The Nature of the Absorbed Soft X-Ray Variations in Compton-thin Type-II Active Galactic Nuclei

Abstract The absorbed soft X-ray (<1 keV) emission from Compton thin type-II active galactic nuclei (AGNs) with neutral absorption columns in the range N H = 1021−23 cm−2 may contain emission from star formation or scattered photons from the primary X-ray emission in Compton-thin circumnuclear gas extending out to ∼1 kpc, or leaky-absorbers along the line of sight allowing a part of the primary AGN emission to manifest in the soft X-rays. In a recent sample study of 20 Compton thin type-II AGN, Laha et al. detected variability in the soft X-ray spectra in 5 sources with timescales <20 years, indicating possibly that the primary AGN emission has leaked through the absorption column. I found that the sources with soft X-ray variability exhibit the lowest absorption column densities (N H ∼ 0.7–1.3 × 1022 cm−2) in the sample.