Open issues in Gamma-Ray Bursts: Polarimetry and dark GRBs

We review some open problems in the physics of afterglows, namely their polarization properties and the existence of dark-faint bursts. Polarization studies yield precious insights in the physical structure and dynamical evolution of GRB jets, revealing their magnetization properties and their energy profile. Polarimetric observations of GRB 020813 already allowed to exclude a homogeneous jet for this event. We then present observations of faint-dark bursts, showing that some of them may be obscured by dust, while others are possibly just intrinsically dim