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Hard X-ray Opacities in the Twisted Magnetospheres of Magnetars

Presentation #110.48 in the session “Stellar/Compact (Poster)”.

Published onApr 01, 2022
Hard X-ray Opacities in the Twisted Magnetospheres of Magnetars

Magnetars are a topical class of neutron stars characterized by strong surface magnetic fields generally exceeding the quantum critical value of 44.1 TeraGauss. High energy photons propagating in the magnetospheres of magnetars can be attenuated by QED processes like photon splitting and magnetic pair creation. In this work we explore the photon opacities due to photon splitting and pair creation in the magnetospheres of magnetars. We consider axi-symmetric, twisted dipole field configurations embedded in the Schwarzschild metric. This work details escape energies, which are the maximum energies for photon transparency that permit propagation to infinity. The photons are emitted from the magnetosphere close to the stellar surface. Special emphasis is given to the case where photons are generated along twisted magnetic field loops, which is directly related to the resonant inverse Compton scattering model for the hard X-ray emission from magnetars. We find that photon splitting puts constraints on the emission region locales and also on the twist angle of the magnetosphere, when accounting for implicit spectral transparency of persistent hard X-ray tail and burst observations of magnetars. We also address polarization signatures that are of interest for future polarimetry missions in the hard X-ray/soft gamma-ray band such as AMEGO.

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