XIPE: the x-ray imaging polarimetry explorer

XIPE, the X-rayImaging PolarimetryExplorer, is a mission dedicated to X-ray Astronomy. At the time of writing XIPE is in a competitive phase A as fourth medium size mission of ESA (M4). It promises to reopen the polarimetrywindow in high energy Astrophysicsafter more than 4 decades thanks to a detector that efficiently exploits the photoelectric effectand to X-ray opticswith large effective area. XIPE uniqueness is time-spectrally-spatially- resolved X-ray polarimetryas a breakthrough in high energy astrophysicsand fundamental physics. Indeed the payloadconsists of three Gas Pixel Detectors at the focus of three X-ray opticswith a total effective area larger than one XMM mirror but with a low weight. The payloadis compatible with the fairing of the Vega launcher. XIPE is designed as an observatory for X-rayastronomers with 75 % of the time dedicated to a Guest Observer competitive programand it is organized as a consortium across Europe with main contributions from Italy, Germany, Spain, United Kingdom, Poland, Sweden.