A resonant absorption line in the ASCA spectrum of NGC 985?

Abstract

We present timing and spectral analyses of the ASCA observation of the Seyfert 1 galaxy NGC 985. The 0.6–10 keV spectrum of this source is complex: large residuals are evident below 1 keV when fitting the spectrum with a power-law model. Fitting a warm absorber model to the 0.6–2.5 keV spectrum gives α = 1.12 ± 0.04, Log N H WA = 21.97 ± 0.08 and LogU = 0.06 ± 0.09, but the residuals continue to show a deficit of counts between 0.9 and 1 keV. Adding an absorption line improves the fit, and the energy of thhe line is consistent with that of Kα NeIX-X resonant absorption lines. Hence, we confirm the presence of an ionized absorber along the line of sight to this source and interpret the further 1 keV spectral feature as the first detection of a strong resonant absorption line associated with this system. The extrapolation of this model above 2.5 keV produces large positive residuals above 3–4 keV. Fitting the data with a broken power law plus warm absorber model gives an acceptable ξ 2 and Δα ∼ 0.5. A narrow iron line at 6.4 keV (quasar frame) of equivalent width 138 −110 +64 eV is also present in the ASCA data.