Systematic Analysis of the Effects of Mode Conversion on Thermal Radiation from Neutron Stars

Akihiro Yatabe, Shoichi Yamada

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    2 Citations (Scopus)

    Abstract

    In this paper, we systematically calculate the polarization in soft X-rays emitted from magnetized neutron stars, which are expected to be observed by next-generation X-ray satellites. Magnetars are one of the targets for these observations. This is because thermal radiation is normally observed in the soft X-ray band, and it is thought to be linearly polarized because of different opacities for two polarization modes of photons in the magnetized atmosphere of neutron stars and the dielectric properties of the vacuum in strong magnetic fields. In their study, Taverna et al. illustrated how strong magnetic fields influence the behavior of the polarization observables for radiation propagating in vacuo without addressing a precise, physical emission model. In this paper, we pay attention to the conversion of photon polarization modes that can occur in the presence of an atmospheric layer above the neutron star surface, computing the polarization angle and fraction and systematically changing the magnetic field strength, radii of the emission region, temperature, mass, and radii of the neutron stars. We confirmed that if plasma is present, the effects of mode conversion cannot be neglected when the magnetic field is relatively weak, B ∼ 1013 G. Our results indicate that strongly magnetized (B ≳ 1014 G) neutron stars are suitable to detect polarizations, but not-so-strongly magnetized (B ∼ 1013 G) neutron stars will be the ones to confirm the mode conversion.

    Original languageEnglish
    Article number185
    JournalAstrophysical Journal
    Volume850
    Issue number2
    DOIs
    Publication statusPublished - 2017 Dec 1

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    Keywords

    • magnetic fields
    • polarization
    • stars: neutron

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

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