The HARPO project (Hermetic ARgon POlarimeter) is a collaboration of groups from LLR ( Ecole Polytechnique & CNRS / IN2P3 ) and IRFU ( CEA Saclay ) that studies the "thin" detector concept in order to perform high performance γ-ray astronomy and polarimetry of cosmic sources. HARPO will enable us to perform gamma-ray astronomy in the MeV - GeV energy range thus bridging the sensitivity gap between Compton and pair telescopes. It will offer an improvement in angular resolution of up to a factor of ten with respect to that of the Fermi LAT. This developement has been possible thanks to successive fundings by CNRS/IN2P3, LabEx PI2O, and the French ANR.

I will present our development of gas time projection chambers (TPC) as high-performance telescopes and polarimeters for cosmic gamma rays converting to e+e-, i.e. in the MeV - GeV energy range.

Focus will be given to the design and the commissionning of our prototype, the datataking on beam, and the analysis of these data (arXiv:1706.06483 submitted to Astroparticle Physics), and the developments towards a balloon flight detector.

Host: Dr. Shaobo WANG