2016/10/27 by R. P. Mignani, R. Mignani, V. Testa +10 · 177 citations
Engineering · Physics and Astronomy · #Astronomical Observations and Instrumentation #Astrophysical Phenomena and Observations #Astrophysics #Birefringence #Galaxy #Laser #Linear polarization #Magnetic field #Neutron star #Optics #Physics #Polarimetry #Polarization (electrochemistry) #Position angle #Pulsars and Gravitational Waves Research #QED vacuum #Scattering #Stars #Vacuum energy #astro-ph.HE
paper · pdf · doi:10.1093/mnras/stw2798
published in Monthly Notices of the Royal Astronomical Society 465(1), 492-500 (Oxford University Press) · 9 pages, 7 figures, accepted for publication on MNRAS
arxiv created 2016/10/27 · openalex publication_date 2016/11/02 · arxiv updated 2016/12/14 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
The ‘Magnificent Seven’ (M7) are a group of radio-quiet isolated neutron stars discovered in the soft X-rays through their purely thermal surface emission. Owing to the large inferred magnetic fields (B ≈ 1013 G), radiation from these sources is expected to be substantially polarized, independently of the mechanism actually responsible for the thermal emission. A large observed polarization degree (PD) is, however, expected only if quantum-electrodynamic (QED) polarization effects are present in the magnetized vacuum around the star. The detection of a strong linearly polarized signal would therefore provide the first observational evidence of QED effects in the strong-field regime. While polarization measurements in the soft X-rays are not feasible yet, optical polarization measurements are within reach also for quite faint targets, like the M7 which have optical counterparts with magnitudes ≈26–28. Here, we report on the measurement of optical linear polarization for the prototype, and brightest member, of the class, RX J1856.5−3754 (V ∼ 25.5), the first ever for one of the M7, obtained with the Very Large Telescope. We measured a PD = 16.43 ± 5.26 per cent and a polarization position angle PA = 145|.∘|39 ± 9|.∘|44, computed east of the North Celestial Meridian. The PD that we derive is large enough to support the presence of vacuum birefringence, as predicted by QED.