Speaker
Description
RX J1856.5-3754 ia a radio-quiet Isolated Neutron Stars (INSs) discovered in the soft X-rays through their purely thermal surface emission. Owing to its large inferred magnetic fields ($B\approx 10^{13}$ G), radiation from this source 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. Here, we report on the measurement of optical linear polarisation for RX J1856.5-3754 ($V\sim 25.5$), obtained with the Very Large Telescope. We measured a polarisation degree $\mathrm{P.D.} =16.43\% \pm5.26\%$, large enough to support the presence of vacuum birefringence, as predicted by QED.
