Published in
arXiv, 2022
DOI: 10.48550/arxiv.2212.12472
American Astronomical Society, Astrophysical Journal, 2(943), p. 129, 2023
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Polarization Properties of the Weakly Magnetized Neutron Star X-Ray Binary GS 1826–238 in the High Soft State
,
Sergio Fabiani ,
Andrea Gnarini ,
Francesco Ursini ,
Carlo Ferrigno ,
Giorgio Matt ,
Juri Poutanen ,
Massimo Cocchi ,
Romana Mikusincova ,
Ruben Farinelli ,
Stefano Bianchi ,
Jari J. E. Kajava ,
Fabio Muleri ,
Celia Sanchez-Fernandez ,
Paolo Soffitta
and other authors.
Abstract
Abstract The launch of the Imaging X-ray Polarimetry Explorer (IXPE) on 2021 December 9 has opened a new window in X-ray astronomy. We report here the results of the first IXPE observation of a weakly magnetized neutron star, GS 1826−238, performed on 2022 March 29–31 when the source was in a high soft state. An upper limit (99.73% confidence level) of 1.3% for the linear polarization degree is obtained over the IXPE 2–8 keV energy range. Coordinated INTEGRAL and NICER observations were carried out simultaneously with IXPE. The spectral parameters obtained from the fits to the broadband spectrum were used as inputs for Monte Carlo simulations considering different possible geometries of the X-ray emitting region. Comparing the IXPE upper limit with these simulations, we can put constraints on the geometry and inclination angle of GS 1826–238.