The high optical polarization in the Be/X-ray binary EXO 2030+375

Abstract

Polarization in classical Be stars results from Thomson scattering of the unpolarized light from the Be star in the circumstellar disc. Theory and observations agree that the maximum degree of polarization from isolated Be stars is < 4%. We report on the first optical polarimetric observations of the Be/X-ray binary EXO\,2030+375. We find that the optical (R band) light is strongly linearly polarized with a degee of polarization of 19%, the highest ever measured either in a classical or Be/X-ray binary. We argue that the interstellar medium cannot account for this high polarization degree and that a substantial amount must be intrinsic to the source. We propose that it may result from the alignment of non-spherical ferromagnetic grains in the Be star disc due to the strong neutron star magnetic field.

to be published in MNRAS

References in corpus (4)

• Non-LTE Monte Carlo Radiative Transfer: II. Non-Isothermal Solutions for Viscous Keplerian Disks
• Outbursts Large and Small from EXO 2030+375
• Be Star Disk Models in Consistent Vertical Hydrostatic Equilibrium
• Recent RXTE/ASM and ROTSEIIId Observations of EXO 2030+375

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• RoboPol: A four-channel optical imaging polarimeter
• Celestial Mechanics and Polarization Optics of the Kordylewski Dust Cloud in the Earth-Moon Lagrange Point L5 Part II. Imaging Polarimetric Observation: New Evidence for the Existence of Kordylewski Dust Cloud
• 2S1553-542: a Be/X-ray binary pulsar on the far side of the Galaxy
• Optical linear polarization of 74 white dwarfs with the RoboPol polarimeter
• GROJ1750-27: a neutron star far behind the Galactic Center switching into the propeller regime
• Catalog of the Galactic population of X-ray pulsars in High-mass X-ray binary systems