Future X-ray Polarimetry of Relativistic Accelerators: PWNe and SNRs

Supernova Remnants and Pulsar Wind Nebulae are among the most significant sources of non-thermal X-rays in the sky, and the closest laboratories where relativistic plasma dynamics and particle acceleration can be investigated. Being strong synchrotron emitters, they are ideal candidates for X-ray polarimetry, and indeed the Crab nebula is up to present the only object where X-ray polarization has been detected with a high level of significance. Future polarimetric measures will likely provide us crucial informations on the level of turbulence that is expected at the particle acceleration sites, together with the spacial and temporal coherence of the magnetic field geometry, enabling us to set stronger constraints on our acceleration models. In PWNe it will also allow us to estimate the level of internal dissipation. I will briefly review the current knowledge on the polarization signatures in SNR/PWNe and I will illustrate what can we hope to achieve with future missions like IXPE/XIPE.