Precision Fe Kα and Fe Kβ Line Spectroscopy of the Seyfert 1.9 Galaxy NGC 2992 with Suzaku

Abstract

Abstract We present detailed time-averaged X-ray spectroscopy in the 0.5–10 keV band of the Seyfert 1.9 galaxy NGC 2992 with the Suzaku X-ray Imaging Spectrometer (XIS). There is an Fe K line emission complex that we model with broad and narrow lines and we show that the intensities of the two components are decoupled at a confidence level $ \gt3\sigma$. The broad line ($\mathrm{EW} = 118^{+32}_{-61} \,\mathrm{eV}$) could originate in an accretion disk (inclined at $ \gt30^{\circ}$). The narrow Fe $\mathrm{K}\alpha$ line ($\mathrm{EW} =163^{+47}_{-26} \,\mathrm{eV}$) is unresolved by the XIS at 99% confidence and likely originates in distant matter. A significant (narrow) Fe $\mathrm{K}\beta$ line is also detected and we describe a new robust method to constrain the ionization state of Fe in the distant line emitter (e.g. the putative obscuring torus). The method does not require any knowledge of possible gravitational and Doppler energy shifts and we deduce that the predominant ionization state of Fe in the distant matter is lower than Fe VIII (at 99% confidence), conservatively taking into account residual calibration uncertainties and theoretical and experimental uncertainties in the Fe K fluorescent line energies. We argue that the narrow Fe $\mathrm{K}\alpha$ and Fe $\mathrm{K}\beta$ lines likely originate in a Compton-thin structure.