Abstract. High-sensitivity observations of cosmic sources are scarce in the gap that lies between the domains in which Compton telescopes and pair telescopes are at their best, i.e. in the energy range ~ 0.1 -- 100 MeV. Also gamma-ray polarimetry, which would be such a powerful diagnostic of the process(es) at work in gamma-ray emitters, in particular related to the intensity and to the homogeneity/turbulence of the magnetic field, has never been achieved with e+e- pairs on cosmic sources. I will present how low-density active targets such as gas detectors can improve on the observation of MeV photons and enable (linear) polarimetry. We have characterized a gas time-projection chamber (TPC) prototype on beam and demonstrated for the first time the polarimetry of a MeV gamma-ray beam with a good dilution factor [Astroparticle Physics 97 (2018) 10].

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