X-rays are particularly suited to probe the physics of extreme objects.However, despite the enormous improvements of X-ray Astronomy in imaging,spectroscopy and timing, polarimetry remains largely unexplored. We propose thephotoelectric polarimeter Gas Pixel Detector (GPD) as an instrument candidateto fill the gap of more than thirty years of lack of measurements. The GPD, inthe focus of a telescope, will increase the sensitivity of orders of magnitude.Moreover, since it can measure the energy, the position, the arrival time andthe polarization angle of every single photon, allows to perform polarimetry ofsubsets of data singled out from the spectrum, the light curve or the image ofsource. The GPD has an intrinsic very fine imaging capability and in this workwe report on the calibration campaign carried out in 2012 at the PANTER X-raytest facility of the Max-Planck-Institut f\"ur extraterrestrische Physik ofGarching (Germany) in which, for the first time, we coupled it to a JET-Xoptics module with a focal length of 3.5 m and an angular resolution of 18arcsec at 4.5 keV. This configuration was proposed in 2012 aboard the X-rayImaging Polarimetry Explorer (XIPE) in response to the ESA call for a smallmission. We derived the imaging and polarimetric performance for extendedsources like Pulsar Wind Nebulae and Supernova Remnants as case studies for theXIPE configuration, discussing also possible improvements by coupling thedetector with advanced optics, having finer angular resolution and largereffective area, to study with more details extended objects.
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