QED effects from the study of polarised light in isolated neutron stars
Intervenant : Roberto Mignani
RX J1856.5-3754 is an Isolated Neutron Stars (INSs) discovered in the soft X-rays through its purely thermal surface emission. Owing to its large inferred magnetic field of ∼10^13 G, radiation from its surface is expected to be substantially polarised, independently on the mechanism actually responsible for the thermal emission. A large observed polarisation degree is, however, expected only if quantum-electrodynamics (QED) polarisation effects are present in the magnetised vacuum around the star. In this talk, I will briefly introduce the observational properties of isolated neutron stars and report on the measurement of optical linear polarisation for RX J1856.5-3754 (V∼25.5) with the Very Large Telescope. We measured a polarisation degree P.D.=16.43%±5.26%, large enough to support the presence of vacuum birefringence, as predicted by QED.