A1 Refereed original research article in a scientific journal
Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1
Authors: Monaca FL, Marco AD, Poutanen J, Bachetti M, Motta SE, Papitto A, Pilia M, Xie F, Bianchi S, Bobrikova A, Costa E, Deng W, Ge M, Illiano G, Jia S, Krawczynski H, Lai EV, Liu K, Mastroserio G, Muleri F, Rankin J, Soffitta P, Veledina A, Ambrosino F, Santo MD, Chen W, Garcia JA, Kaaret P, Russell TD, Wei W, Zhang S, Zuo C, Arzoumanian Z, Cocchi M, Gnarini A, Farinelli R, Gendreau K, Ursini F, Weisskopf MC, Zane S, Agudo I, Antonelli LA, Baldini L, Baumgartner WH, Bellazzini R, Bongiorno SD, Bonino R, Brez A, Bucciantini N, Capitanio F, Castellano S, Cavazzuti E, Chen C, Ciprini S, Rosa AD, Monte ED, Gesu LD, Lalla ND, Donnarumma I, Doroshenko V, Dovčiak M, Ehlert SR, Enoto T, Evangelista Y, Fabiani S, Ferrazzoli R, Gunji S, Hayashida K, Heyl J, Iwakiri W, Jorstad SG, Karas V, Kislat F, Kitaguchi T, Kolodziejczak JJ, Latronico L, Liodakis I, Maldera S, Manfreda A, Marin F, Marinucci A, Marscher AP, Marshall HL, Massaro F, Matt G, Mitsuishi I, Mizuno T, Negro M, Ng C, O’Dell SL, Omodei N, Oppedisano C, Pavlov GG, Peirson AL, Perri M, Pesce-Rollins M, Petrucci P, Possenti A, Puccetti S, Ramsey BD, Ratheesh A, Roberts OJ, Romani RW, Sgrò C, Slane P, Spandre G, Swartz DA, Tamagawa T, Tavecchio F, Taverna R, Tawara Y, Tennant AF, Thomas NE, Tombesi F, Trois A, Tsygankov SS, Turolla R, Vink J, Wu K; IXPE Collaboration
Publisher: Institute of Physics Publishing
Publication year: 2024
Journal: Astrophysical Journal Letters
Journal name in source: The Astrophysical Journal Letters
Article number: L11
Volume: 960
Issue: 2
eISSN: 2041-8213
DOI: https://doi.org/10.3847/2041-8213/ad132d
Web address : https://dx.doi.org/10.3847/2041-8213/ad132d
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/386857976
Preprint address: https://arxiv.org/abs/2311.06359
The Imaging X-ray Polarimetry Explorer measured with high significance the X-ray polarization of the brightest Z-source, Sco X-1, resulting in the nominal 2–8 keV energy band in a polarization degree of 1.0% ± 0.2% and a polarization angle of 8° ± 6° at a 90% confidence level. This observation was strictly simultaneous with observations performed by NICER, NuSTAR, and Insight-HXMT, which allowed for a precise characterization of its broadband spectrum from soft to hard X-rays. The source has been observed mainly in its soft state, with short periods of flaring. We also observed low-frequency quasiperiodic oscillations. From a spectropolarimetric analysis, we associate a polarization to the accretion disk at <3.2% at 90% confidence level, compatible with expectations for an electron scattering dominated optically thick atmosphere at the Sco X-1 inclination of ∼44°; for the higher-energy Comptonized component, we obtain a polarization of 1.3% ± 0.4%, in agreement with expectations for a slab of Thomson optical depth of ∼7 and an electron temperature of ∼3 keV. A polarization rotation with respect to previous observations by OSO-8 and PolarLight, and also with respect to the radio-jet position angle, is observed. This result may indicate a variation of the polarization with the source state that can be related to relativistic precession or a change in the corona geometry with the accretion flow.
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