The 1.5 Ms Observing Campaign on IRAS 13224-3809: X-ray Spectral Analysis I

Abstract

We present a detailed spectral analysis of the recent 1.5\,Ms XMM-Newton observing campaign on the narrow line Seyfert 1 galaxy IRAS~13224$-$3809, taken simultaneously with 500\,ks of NuSTAR data. The X-ray lightcurve shows three flux peaks, registering at about 100 times the minimum flux seen during the campaign, and rapid variability with a time scale of kiloseconds. The spectra are well fit with a primary powerlaw continuum, two relativistic-blurred reflection components from the inner accretion disk with very high iron abundance, and a simple blackbody-shaped model for the remaining soft excess. The spectral variability is dominated by the power law continuum from a corona region within a few gravitational radii from the black hole. Additionally, blueshifted Ne \textsc{x}, Mg \textsc{xii}, Si \textsc{xiv} and S \textsc{xvi} absorption lines are identified in the stacked low-flux spectrum, confirming the presence of a highly ionized outflow with velocity up to $v=0.267$ and $0.225$\,c. We fit the absorption features with \texttt{xstar} models and find a relatively constant velocity outflow through the whole observation. Finally, we replace the \texttt{bbody} and supersolar abundance reflection models by fitting the soft excess successfully with the extended reflection model \texttt{relxillD}, which allows for higher densities than the standard \texttt{relxill} model. This returns a disk electron density $n_{\mathrm{e}}>10^{18.7}$\,cm${}^{-3}$ and lowers the iron abundance from $Z_{\mathrm{Fe}}=24_{-4}^{+3}{Z}_{\odot }$ with $n_{\mathrm{e}}\equiv 10^{15}$\,cm${}^{-3}$ to $Z_{\mathrm{Fe}}=6.6_{-2.1}^{+0.8}{Z}_{\odot }$.

18 pages, 14 figures. Accepted by MNRAS