Simultaneous NuSTAR – XMM-Newton observations of AGN Abstract Joint X-ray observations of the satellites XMM-Newton and NuSTAR have become the main tool to study the 6.4 keV iron K alpha line emission in the direct environment of black holes. The soft (XMM-Newton) and hard (NuSTAR) X-ray spectra together allow determining the continuum, absorption, reflection and emission lines. In order to get better results in future, the present study aims to help improving the cross-calibration by analyzing all publicly available simultaneous NuSTAR – XMM-Newton observations in a coherent way. Andrea Gokus1,2, Norbert Schartel2, Maria Santos-Lleo2, Jörn Wilms1, Thomas Dauser1, Felix Fürst3, Ralf Ballhausen1 XMM-Newton Artist's impression of XMM-Newton ©ESA Launched in 1999, ESA's XMM-Newton observes the energy range from 0.2 to 12 keV with the European Photon Imaging Camera (EPIC) using a Wolter type I telescope. Additionally it has an Optical Monitor (OM) and a Reflection Grating Spectrometer (RGS) onboard. NuSTAR NuSTAR, launched by NASA in 2012, is the first focusing high-energy instrument in space. It uses Wolter type I approximation optics and two semiconductor detectors (FPMA, FPMB) to observe hard X-rays from 3 to 79 keV. The 10 m long mast was deployed in space. Artist's impression of NuSTAR ©NASA 1Dr. Karl Remeis Observatory & Erlangen Centre for Astroparticle Physics (ECAP), Universität Erlangen-Nürnberg, Sternwartstraße 7, 96049 Bamberg, Germany 2European Space Astronomy Center (ESAC), ESA, 28692 Villanueva de la Cañada, Madrid, Spain 3Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA Why simultaneous observations? Performing observations with XMM- Newton and NuSTAR together has the main advantage that they have an energy overlap between 3 and 12 keV, which includes the region of the iron K alpha line. The emission features around 6.4 keV allow the analysis of relativistic line broadening near black hole systems, when the underlying continuum is well known. This can be achieved with a simultaneous obser- vation by both satellites, since their effective areas overlap from 3 to 12 keV. Comparison of the effective area of the XMM-Newton satellite (black) and the NuSTAR satellite (red). Comparison of XMM-Newton and NuSTAR data Ideally, with a perfect calibration, a model for a certain X-ray spectrum should give the same results when applied to both XMM-Newton and NuSTAR data. Since the perfect calibration is not possible to achieve, calibration uncertainties make discrepancies appear in the data analysis and the determination of astrophysical values is impacted. Those discrepancies can be shown, e.g. by fitting a model to an XMM- Newton spectrum and then comparing the strictly simultaneous NuSTAR spectrum with this model (see ratio plots below; black: XMM-Newton EPIC PN data, red: NuSTAR FPMA data, green: NuSTAR FPMB data; the data has been binned for clarity). The used models contain a powerlaw and the X-ray absorption model tbnew (Wilms et al., 2000; http://pulsar.sternwarte.uni-erlangen.de/wilms/research/tbabs/). If the source shows relativistic reflections effects, the reflection model relxill (Dauser & Garcia et al., 2014) is included as well. Ark 120 Seyfert 1 galaxy z = 0.0327 3C 273 Blazar z = 0.158 MCG-6-30-15 Seyfert 1 galaxy z = 0.008 Swift J2127.4+5654 Narrow-Line Seyfert 1 Galaxy z = 0.0144 3C 120 Broad-Line Radio Galaxy z = 0.0336 ΔΓ EPN-FPMA 0.135 ± 0.004 EPN-FPMB 0.128 ± 0.007 Results & Conclusions A difference between the photon indices for data from both satellites can be found when fitting the spectra from 3 to 10 keV simultaneously. This has been done with a sub-sample of 12 observations of 6 AGN. The difference can be plotted over the flux of the different sources in order to show that ΔΓ is independent of the flux and therefore not due to pile-up. The mean differences for EPN-FPMA and EPN-FPMB are: These preliminary results show a potential cross-calibrati