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

J. Jiang, M. L. Parker, A. C. Fabian, W. N. Alston, D. J. K. Buisson, E. M. Cackett, C.-Y. Chiang, T. Dauser, L. C. Gallo, J. A. García, F. A. Harrison, A. M. Lohfink, B. De Marco, E. Kara, J. M. Miller, G. Miniutti, C. Pinto, D. J. Walton and D. R. Wilkins, 2018, MNRAS 477, 3711

We present a detailed spectral analysis of the recent 1.5Ms XMM-Newton observing campaign on the narrow line Seyfert 1 galaxy IRAS 13224−3809, taken simultaneously with 500ks 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 X, Mg XII, Si XIV and S 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 0.225c. We fit the absorption features with \texttt models and find a relatively constant velocity outflow through the whole observation. Finally, we replace the \texttt and supersolar abundance reflection models by fitting the soft excess successfully with the extended reflection model \texttt, which allows for higher densities than the standard \texttt model. This returns a disk electron density ne>1018.7cm−3 and lowers the iron abundance from ZFe=24+3−4Z⊙ with ne≡1015cm−3 to ZFe=6.6+0.8−2.1Z⊙.