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IXPE Observations of the Quintessential Wind-accreting X-Ray Pulsar Vela X-1

Forsblom, Sofia V; Poutanen, Juri; Tsygankov, Sergey S; Bachetti, Matteo; Marco, Alessandro Di; Doroshenko, Victor; Heyl, Jeremy; ... IXPE Collaboration; + view all (2023) IXPE Observations of the Quintessential Wind-accreting X-Ray Pulsar Vela X-1. The Astrophysical Journal Letters , 947 (2) , Article L20. 10.3847/2041-8213/acc391. Green open access

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Abstract

The radiation from accreting X-ray pulsars was expected to be highly polarized, with some estimates for the polarization degree of up to 80%. However, phase-resolved and energy-resolved polarimetry of X-ray pulsars is required in order to test different models and to shed light on the emission processes and the geometry of the emission region. Here we present the first results of the observations of the accreting X-ray pulsar Vela X-1 performed with the Imaging X-ray Polarimetry Explorer. Vela X-1 is considered to be the archetypal example of a wind-accreting, high-mass X-ray binary system, consisting of a highly magnetized neutron star accreting matter from its supergiant stellar companion. The spectropolarimetric analysis of the phase-averaged data for Vela X-1 reveals a polarization degree (PD) of 2.3% ± 0.4% at the polarization angle (PA) of −47.°3 ± 5.°4. A low PD is consistent with the results obtained for other X-ray pulsars and is likely related to the inverse temperature structure of the neutron star atmosphere. The energy-resolved analysis shows the PD above 5 keV reaching 6%–10% and a ∼90° difference in the PA compared to the data in the 2–3 keV range. The phase-resolved spectropolarimetric analysis finds a PD in the range 0%–9% with the PA varying between −80° and 40°.

Type: Article
Title: IXPE Observations of the Quintessential Wind-accreting X-Ray Pulsar Vela X-1
Open access status: An open access version is available from UCL Discovery
DOI: 10.3847/2041-8213/acc391
Publisher version: https://dx.doi.org/10.3847/2041-8213/acc391
Language: English
Additional information: Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence (http://creativecommons.org/licenses/by/4.0/). Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Keywords: Pulsars; Starlight polarization; Neutron stars; High mass x-ray binary stars; Magnetic fields; Accretion
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10168684
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