Highly Ionized Iron Absorption Lines from Outflowing Gas in the X-Ray Spectrum of NGC 1365

Abstract

We present the discovery of four absorption lines in the X-ray spectrum of the Seyfert galaxy NGC 1365, at energies between 6.7 and 8.3 keV. The lines are detected with high statistical confidence (from >20 σ for the strongest to ~4 σ for the weakest) in two XMM-Newton observations 60 ks long. We also detect the same lines, with a lower signal-to-noise ratio (but still >2 σ for each line), in two previous shorter (~10 ks) XMM-Newton observations. The spectral analysis identifies these features as Fe XXV and Fe XXVI Kα and Kβ lines, outflowing with velocities varying between ~1000 and ~5000 km s^-1 among the observations. These are the highest quality detections of such lines so far. The high equivalent widths [EW(Kα)~100 eV] and the Kα/Kβ ratios imply that the lines are due to absorption of the AGN continuum by a highly ionized gas with column density N_H~5×10²³ cm^-2 at a distance of ~(50-100)R_S from the continuum source.