eprintid: 10197387
rev_number: 11
eprint_status: archive
userid: 699
dir: disk0/10/19/73/87
datestamp: 2024-09-20 10:53:56
lastmod: 2024-09-20 10:53:56
status_changed: 2024-09-20 10:53:56
type: article
metadata_visibility: show
sword_depositor: 699
creators_name: Kelly, Ruth ME
creators_name: González-Caniulef, Denis
creators_name: Zane, Silvia
creators_name: Turolla, Roberto
creators_name: Taverna, Roberto
title: X-ray polarisation signatures in bombarded magnetar atmospheres
ispublished: inpress
divisions: UCL
divisions: B04
divisions: C06
divisions: F63
keywords: Polarisation, radiative transfer, stars: atmospheres, stars: magnetars
note: Copyright © The Author(s) 2024. Published by Oxford University Press on behalf of Royal Astronomical Society.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
abstract: Magnetars are neutron stars that host huge, complex magnetic fields which require supporting currents to flow along the closed field lines. This makes magnetar atmospheres different from those of passively cooling neutron stars because of the heat deposited by backflowing charges impinging on the star surface layers. This particle bombardment is expected to imprint the spectral and, even more, the polarisation properties of the emitted thermal radiation. We present solutions for the radiative transfer problem for bombarded plane-parallel atmospheres in the high magnetic field regime. The temperature profile is assumed a priori, and selected in such a way to reflect the varying rate of energy deposition in the slab (from the impinging currents and/or from the cooling crust). We find that thermal X–ray emission powered entirely by the energy released in the atmosphere by the magnetospheric back–bombardment is linearly polarised and X-mode dominated, but its polarisation degree is significantly reduced (down to 10%–50%) when compared with that expected from a standard atmosphere heated only from the cooling crust below. By increasing the fraction of heat flowing in from the crust the polarisation degree of the emergent radiation increases, first at higher energies (∼10 keV) and then in the entire soft X-ray band. We use our models inside a ray-tracing code to derive the expected emission properties as measured by a distant observer and compare our results with recent IXPE observations of magnetar sources.
date: 2024-09-17
date_type: published
publisher: Wiley-Blackwell
official_url: https://doi.org/10.1093/mnras/stae2163
oa_status: green
full_text_type: other
language: eng
primo: open
primo_central: open_green
verified: verified_manual
elements_id: 2314050
doi: 10.1093/mnras/stae2163
lyricists_name: Zane, Silvia
lyricists_id: SZANE58
actors_name: Zane, Silvia
actors_id: SZANE58
actors_role: owner
funding_acknowledgements: ST/W507891/1 [UKRI/STFC]
full_text_status: public
publication: Monthly Notices of the Royal Astronomical Society
article_number: stae2163
issn: 0035-8711
citation:        Kelly, Ruth ME;    González-Caniulef, Denis;    Zane, Silvia;    Turolla, Roberto;    Taverna, Roberto;      (2024)    X-ray polarisation signatures in bombarded magnetar atmospheres.                   Monthly Notices of the Royal Astronomical Society      , Article stae2163.  10.1093/mnras/stae2163 <https://doi.org/10.1093/mnras%2Fstae2163>.    (In press).    Green open access   
 
document_url: https://discovery.ucl.ac.uk/id/eprint/10197387/1/Zane_stae2163.pdf