A1 Refereed original research article in a scientific journal
Expected polarization properties of nonmagnetized CCOs
Authors: Suleimanov Valery F, Poutanen Juri, Doroshenko Victor, Werner Klaus
Publisher: EDP SCIENCES S A
Publication year: 2023
Journal: Astronomy and Astrophysics
Journal name in source: ASTRONOMY & ASTROPHYSICS
Journal acronym: ASTRON ASTROPHYS
Article number: A15
Volume: 673
Number of pages: 9
ISSN: 0004-6361
DOI: https://doi.org/10.1051/0004-6361/202346092
Publication's open availability at the time of reporting: Open Access
Publication channel's open availability : Open Access publication channel
Web address : https://doi.org/10.1051/0004-6361/202346092
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/179787078
Self-archived copy's licence: CC BY
Self-archived copy's version: Publisher`s PDF
Central compact objects (CCOs) are neutron stars found close to the center of some supernova remnants. A certain number of them are presumably covered by carbon envelopes. Their unpulsed thermal X-ray emission can originate either from the entire surface covered by a carbon atmosphere or alternatively from a nonuniformly emitting hydrogen atmosphere. However, the latter scenario appears unlikely given the available upper limits on the amplitude of pulsations. Here we explore a possibility to further discriminate between the two scenarios using X-ray polarimetric observations. We compute the polarization degree (PD) for nonmagnetized pure-carbon and pure-hydrogen atmospheres with effective temperatures of between 1 and 6 MK and find that it can reach up to 25% and 40% for hydrogen and carbon atmospheres, respectively, in the photon energy band 1-10 keV. However, given the available constraints on possible inhomogeneities of the temperature distribution deduced from models of the X-ray spectrum of the CCO in HESS J1731-347, the integrated PD appears to be very low for both carbon (<0.25%) and hydrogen (a few percent) compositions in the energy band of 2-8 keV covered by the recently launched Imaging X-ray Polarimetry Explorer. We therefore conclude that polarization from CCOs is not expected to be detectable by current facilities, but future detection would strongly support nonuniform hydrogen composition models.
Keywords:
methods: numerical, radiative transfer, stars: atmospheres, X-rays: stars
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