Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1

DOI: 
10.3847/2041-8213/ad132d
Publication date: 
11/01/2024
Main author: 
La Monaca, Fabio
IAA authors: 
Agudo, Iván
Authors: 
La Monaca, Fabio;Di Marco, Alessandro;Poutanen, Juri;Bachetti, Matteo;Motta, Sara Elisa;Papitto, Alessandro;Pilia, Maura;Xie, Fei;Bianchi, Stefano;Bobrikova, Anna;Costa, Enrico;Deng, Wei;Ge, Ming-Yu;Illiano, Giulia;Jia, Shu-Mei;Krawczynski, Henric;Lai, Eleonora Veronica;Liu, Kuan;Mastroserio, Guglielmo;Muleri, Fabio;Rankin, John;Soffitta, Paolo;Veledina, Alexandra;Ambrosino, Filippo;Del Santo, Melania;Chen, Wei;Garcia, Javier A.;Kaaret, Philip;Russell, Thomas D.;Wei, Wen-Hao;Zhang, Shuang-Nan;Zuo, Chao;Arzoumanian, Zaven;Cocchi, Massimo;Gnarini, Andrea;Farinelli, Ruben;Gendreau, Keith;Ursini, Francesco;Weisskopf, Martin C.;Zane, Silvia;Agudo, Iván;Antonelli, Lucio A.;Baldini, Luca;Baumgartner, Wayne H.;Bellazzini, Ronaldo;Bongiorno, Stephen D.;Bonino, Raffaella;Brez, Alessandro;Bucciantini, Niccolò;Capitanio, Fiamma;Castellano, Simone;Cavazzuti, Elisabetta;Chen, Chien-Ting;Ciprini, Stefano;De Rosa, Alessandra;Del Monte, Ettore;Di Gesu, Laura;Di Lalla, Niccolò;Donnarumma, Immacolata;Doroshenko, Victor;Dovčiak, Michal;Ehlert, Steven R.;Enoto, Teruaki;Evangelista, Yuri;Fabiani, Sergio;Ferrazzoli, Riccardo;Gunji, Shuichi;Hayashida, Kiyoshi;Heyl, Jeremy;Iwakiri, Wataru;Jorstad, Svetlana G.;Karas, Vladimir;Kislat, Fabian;Kitaguchi, Takao;Kolodziejczak, Jeffery J.;Latronico, Luca;Liodakis, Ioannis;Maldera, Simone;Manfreda, Alberto;Marin, Frédéric;Marinucci, Andrea;Marscher, Alan P.;Marshall, Herman L.;Massaro, Francesco;Matt, Giorgio;Mitsuishi, Ikuyuki;Mizuno, Tsunefumi;Negro, Michela;Ng, Chi-Yung;O'Dell, Stephen L.;Omodei, Nicola;Oppedisano, Chiara;Pavlov, George G.;Peirson, Abel L.;Perri, Matteo;Pesce-Rollins, Melissa;Petrucci, Pierre-Olivier;Possenti, Andrea;Puccetti, Simonetta;Ramsey, Brian D.;Ratheesh, Ajay;Roberts, Oliver J.;Romani, Roger W.;Sgrò, Carmelo;Slane, Patrick;Spandre, Gloria;Swartz, Douglas A.;Tamagawa, Toru;Tavecchio, Fabrizio;Taverna, Roberto;Tawara, Yuzuru;Tennant, Allyn F.;Thomas, Nicholas E.;Tombesi, Francesco;Trois, Alessio;Tsygankov, Sergey S.;Turolla, Roberto;Vink, Jacco;Wu, Kinwah;IXPE Collaboration
Journal: 
The Astrophysical Journal
Publication type: 
Article
Volume: 
960
Pages: 
L11
Abstract: 
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.
Database: 
ADS
SCOPUS
URL: 
https://ui.adsabs.harvard.edu/#abs/2024ApJ...960L..11L/abstract
ADS Bibcode: 
2024ApJ...960L..11L
Keywords: 
Polarimetry;Spectropolarimetry;Neutron stars;Accretion;Stellar accretion disks;Low-mass x-ray binary stars;X-ray telescopes;1278;1973;1108;14;1579;939;1825;Astrophysics - High Energy Astrophysical Phenomena