Expected polarization properties of nonmagnetized CCOs



: Suleimanov Valery F, Poutanen Juri, Doroshenko Victor, Werner Klaus

Publisher: EDP SCIENCES S A

: 2023

: Astronomy and Astrophysics

: ASTRONOMY & ASTROPHYSICS

: ASTRON ASTROPHYS

:  A15

: 673

: 9

: 0004-6361

DOI: https://doi.org/10.1051/0004-6361/202346092

: https://doi.org/10.1051/0004-6361/202346092

: https://research.utu.fi/converis/portal/detail/Publication/179787078


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.

Last updated on 2024-26-11 at 21:19