X-ray pulsar GRO J1008−57 as an orthogonal rotator

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2302.06680.pdf (1.47 MB)

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https://arxiv.org/abs/2302.06680

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https://doi.org/10.48550/arXiv.2302.06680
 http://hdl.handle.net/11603/27025

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UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)
UMBC Faculty Collection

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https://orcid.org/0000-0002-6548-5622

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2023-02-13

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journal articles
preprints
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract

X-ray polarimetry is a unique way to probe geometrical configuration of highly-magnetized accreting neutron stars (X-ray pulsars). GRO J1008−57 is the first transient X-ray pulsar observed at two different flux levels by the Imaging X-ray Polarimetry Explorer (IXPE) during its outburst in November 2022. The polarization properties were found to be independent of the source luminosity, with the polarization degree varying between non-detection to about 15% over the pulse phase. Fitting the phase-resolved spectro-polarimetric data with the rotating vector model allowed us to estimate the pulsar inclination (130° , which is in good agreement with the orbital inclination), the position angle (75° ) of the pulsar spin axis, and the magnetic obliquity (∼ 74° ). This makes GRO J1008−57 the first confidently identified X-ray pulsar as a nearly orthogonal rotator. The results are discussed in the context of the neutron star atmosphere models and theories of pulsars’ axis alignment.