Abstract: With the launch of IXPE at the end of 2021, we have entered the era of X-ray polarization. IXPE is more than one thousand times more sensitive that previous observations giving us “first (polarized) light” images of hundreds of X-ray sources. Looking as these objects in an essentially new way for the very first time has been exhilarating. I will focus in particular on the observations of accreting X-ray pulsars which despite complicated magnetic field and emission geometries with only a single exception exhibit very simple changes in the polarization direction as the stars rotate. This straightforward evolution with spin results from the first (yet still unverified) prediction of QED that a magnetic field even in vacuum induces an index of refraction: vacuum birefringence. The observations of the prototypical X-ray pulsar Hercules X-1 reveal the interior of the neutron star, while observations of the supercritical accretor LS V +44 17/RX J0440.9+4431 show complexity of the emitting accretion flow can produce more complicated polarization patterns.
Polarized Radiation from X-Ray Pulsars
Jeremy Heyl (University of British Columbia) // September 5, 2024
Abstract: With the launch of IXPE at the end of 2021, we have entered the era of X-ray polarization. IXPE is more than one thousand times more sensitive that previous observations giving us “first (polarized) light” images of hundreds of X-ray sources. Looking as these objects in an essentially new way for the very first time has been exhilarating. I will focus in particular on the observations of accreting X-ray pulsars which despite complicated magnetic field and emission geometries with only a single exception exhibit very simple changes in the polarization direction as the stars rotate. This straightforward evolution with spin results from the first (yet still unverified) prediction of QED that a magnetic field even in vacuum induces an index of refraction: vacuum birefringence. The observations of the prototypical X-ray pulsar Hercules X-1 reveal the interior of the neutron star, while observations of the supercritical accretor LS V +44 17/RX J0440.9+4431 show complexity of the emitting accretion flow can produce more complicated polarization patterns.