%0 Journal Article %@ 2041-8205 %A La Monaca, F %A Di Marco, A %A Poutanen, J %A Bachetti, M %A Motta, SE %A Papitto, A %A Pilia, M %A Xie, F %A Bianchi, S %A Bobrikova, A %A Costa, E %A Deng, W %A Ge, MY %A Illiano, G %A Jia, SM %A Krawczynski, H %A Lai, EV %A Liu, K %A Mastroserio, G %A Muleri, F %A Rankin, J %A Soffitta, P %A Veledina, A %A Ambrosino, F %A Del Santo, M %A Chen, W %A Garcia, JA %A Kaaret, P %A Russell, TD %A Wei, WH %A Zhang, SN %A Zuo, C %A Arzoumanian, Z %A Cocchi, M %A Gnarini, A %A Farinelli, R %A Gendreau, K %A Ursini, F %A Weisskopf, MC %A Zane, S %A Agudo, I %A Antonelli, LA %A Baldini, L %A Baumgartner, WH %A Bellazzini, R %A Bongiorno, SD %A Bonino, R %A Brez, A %A Bucciantini, N %A Capitanio, F %A Castellano, S %A Cavazzuti, E %A Chen, CT %A Ciprini, S %A De Rosa, A %A Del Monte, E %A Di Gesu, L %A Di Lalla, N %A Donnarumma, I %A Doroshenko, V %A Dovčiak, M %A Ehlert, SR %A Enoto, T %A Evangelista, Y %A Fabiani, S %A Ferrazzoli, R %A Gunji, S %A Hayashida, K %A Heyl, J %A Iwakiri, W %A Jorstad, SG %A Karas, V %A Kislat, F %A Kitaguchi, T %A Kolodziejczak, JJ %A Latronico, L %A Liodakis, I %A Maldera, S %A Manfreda, A %A Marin, F %A Marinucci, A %A Marscher, AP %A Marshall, HL %A Massaro, F %A Matt, G %A Mitsuishi, I %A Mizuno, T %A Negro, M %A Ng, CY %A O’Dell, SL %A Omodei, N %A Oppedisano, C %A Pavlov, GG %A Peirson, AL %A Perri, M %A Pesce-Rollins, M %A Petrucci, PO %A Possenti, A %A Puccetti, S %A Ramsey, BD %D 2024 %F discovery:10186104 %J The Astrophysical Journal Letters %N 2 %T Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1 %U https://discovery.ucl.ac.uk/id/eprint/10186104/ %V 960 %X 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. %Z Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence, https://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.