A1 Refereed original research article in a scientific journal
Magnetospheric return-current-heated atmospheres of rotation-powered millisecond pulsars
Authors: Tuomo Salmi, Valery F. Suleimanov, Joonas Nättilä, Juri Poutanen
Publisher: EDP SCIENCES S A
Publication year: 2020
Journal: Astronomy and Astrophysics
Journal name in source: ASTRONOMY & ASTROPHYSICS
Journal acronym: ASTRON ASTROPHYS
Article number: ARTN A15
Volume: 641
Number of pages: 13
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202037824
Self-archived copy’s web address: https://arxiv.org/abs/2002.11427
We computed accurate atmosphere models of rotation-powered millisecond pulsars in which the polar caps of a neutron star (NS) are externally heated by magnetospheric return currents. The external ram pressure, energy losses, and stopping depth of the penetrating charged particles were computed self-consistently with the atmosphere model, instead of assuming a simplified deep-heated atmosphere in radiative equilibrium. We used exact Compton scattering formalism to model the properties of the emergent X-ray radiation. The deep-heating approximation was found to be valid only if most of the heat originates from ultra-relativistic bombarding particles with Lorentz factors of gamma greater than or similar to 100. In the opposite regime, the atmosphere attains a distinct two-layer structure with an overheated optically thin skin on top of an optically thick cool plasma. The overheated skin strongly modifies the emergent radiation: It produces a Compton-upscattered high-energy tail in the spectrum and alters the radiation beaming pattern from limb darkening to limb brightening for emitted hard X-rays. This kind of drastic change in the emission properties can have a significant impact on the inferred NS pulse profile parameters as performed, for example, by Neutron star Interior Composition ExploreR. Finally, the connection between the energy distribution of the return current particles and the atmosphere emission properties offers a new tool to probe the exact physics of pulsar magnetospheres.
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