The 1.5 Ms observing campaign on IRAS 13224−3809 – I. X-ray spectral analysis

Abstract

We present a detailed spectral analysis of the recent 1.5\\,Ms XMM-Newton\nobserving campaign on the narrow line Seyfert 1 galaxy IRAS~13224$-$3809, taken\nsimultaneously with 500\\,ks of NuSTAR data. The X-ray lightcurve shows three\nflux peaks, registering at about 100 times the minimum flux seen during the\ncampaign, and rapid variability with a time scale of kiloseconds. The spectra\nare well fit with a primary powerlaw continuum, two relativistic-blurred\nreflection components from the inner accretion disk with very high iron\nabundance, and a simple blackbody-shaped model for the remaining soft excess.\nThe spectral variability is dominated by the power law continuum from a corona\nregion within a few gravitational radii from the black hole. Additionally,\nblueshifted Ne \\textsc{x}, Mg \\textsc{xii}, Si \\textsc{xiv} and S \\textsc{xvi}\nabsorption lines are identified in the stacked low-flux spectrum, confirming\nthe presence of a highly ionized outflow with velocity up to $v= 0.267$ and\n$0.225$\\,c. We fit the absorption features with \\texttt{xstar} models and find\na relatively constant velocity outflow through the whole observation. Finally,\nwe replace the \\texttt{bbody} and supersolar abundance reflection models by\nfitting the soft excess successfully with the extended reflection model\n\\texttt{relxillD}, which allows for higher densities than the standard\n\\texttt{relxill} model. This returns a disk electron density $n_{\\rm\ne}>10^{18.7}$\\,cm$^{-3}$ and lowers the iron abundance from $Z_{\\rm\nFe}=24^{+3}_{-4}Z_\\odot$ with $n_{\\rm e}\\equiv10^{15}$\\,cm$^{-3}$ to $Z_{\\rm\nFe}=6.6^{+0.8}_{-2.1}Z_\\odot$.\n