IZw1 observed with XMM-Newton: Low-energy spectral complexity, iron lines, and hard X-ray flares

TL;DR

This study analyzes a 20 ks XMM-Newton observation of the Seyfert galaxy IZw1, revealing complex soft X-ray absorption, broad iron lines, and a hard X-ray flare that causes spectral variability likely originating from the accretion disc corona.

Contribution

First detailed X-ray spectral and timing analysis of IZw1 showing complex spectral features and flare-induced variability, suggesting coronal origin of the flare.

Findings

Detection of complex soft absorption and Fe Kalpha emission.

Observation of a strong, hard X-ray flare with spectral hardening.

Iron line strength varies inversely with flare activity.

Abstract

We present a 20 ks XMM-Newton observation of the prototypical Narrow-Line Seyfert 1 galaxy IZw1. The best-fit model to the data is a double blackbody plus a dominant power-law, on which complex soft absorption (possibly a blended edge or absorption lines) and/or OVII emission are superimposed, as well as strong Fe Kalpha emission. The iron feature in the high-energy spectra appears broad; however, on close examination of the EPIC pn data, there exists the possibility that the broad emission feature can be attributed to a neutral Fe Kalpha line in addition to a blend of He- and H-like Fe Kalpha lines. The light curve shows a strong, hard X-ray flare concentrated in the 3-12 keV band. The flare appears to induce spectral variability, showing spectral hardening to be occuring as the flare intensifies. A detailed examination suggests that the spectral variability is most likely due to an increase in the 3-12 keV flux relative to the soft flux during the flare. A difference spectrum and complete modelling of the flare and non-flare spectra show intrinsic changes only in the normalisation of the continuum components and not in their shape parameters. The timing results are consistent with the flare originating in the accretion disc corona. The iron emission line(s) do not appear to respond to changes in the continuum flux during the flare; the iron lines are stronger in equivalent width during the low-flux (non-flare) states, and weaker during the flare.