X-Ray Polarized View of the Accretion Geometry in the X-Ray Binary Circinus X-1
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Published:2024-01-01
Issue:1
Volume:961
Page:L8
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ISSN:2041-8205
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Container-title:The Astrophysical Journal Letters
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language:
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Short-container-title:ApJL
Author:
Rankin JohnORCID, La Monaca FabioORCID, Di Marco AlessandroORCID, Poutanen JuriORCID, Bobrikova AnnaORCID, Kravtsov VadimORCID, Muleri FabioORCID, Pilia MauraORCID, Veledina AlexandraORCID, Fender RobORCID, Kaaret PhilipORCID, Kim Dawoon E.ORCID, Marinucci AndreaORCID, Marshall Herman L.ORCID, Papitto AlessandroORCID, Tennant Allyn F.ORCID, Tsygankov Sergey S.ORCID, Weisskopf Martin C.ORCID, Wu KinwahORCID, Zane SilviaORCID, Ambrosino FilippoORCID, Farinelli RubenORCID, Gnarini AndreaORCID, Agudo IvánORCID, Antonelli Lucio A.ORCID, Bachetti MatteoORCID, Baldini LucaORCID, Baumgartner Wayne H.ORCID, Bellazzini RonaldoORCID, Bianchi StefanoORCID, Bongiorno Stephen D.ORCID, Bonino RaffaellaORCID, Brez AlessandroORCID, Bucciantini NiccolòORCID, Capitanio FiammaORCID, Castellano SimoneORCID, Cavazzuti ElisabettaORCID, Chen Chien-TingORCID, Ciprini StefanoORCID, Costa EnricoORCID, De Rosa AlessandraORCID, Del Monte EttoreORCID, Di Gesu LauraORCID, Di Lalla NiccolòORCID, Donnarumma ImmacolataORCID, Doroshenko VictorORCID, Dovčiak MichalORCID, Ehlert Steven R.ORCID, Enoto TeruakiORCID, Evangelista YuriORCID, Fabiani SergioORCID, Ferrazzoli RiccardoORCID, Garcia Javier A.ORCID, Gunji ShuichiORCID, Hayashida Kiyoshi, Heyl JeremyORCID, Iwakiri WataruORCID, Jorstad Svetlana G.ORCID, Karas VladimirORCID, Kislat FabianORCID, Kitaguchi Takao, Kolodziejczak Jeffery J.ORCID, Krawczynski HenricORCID, Latronico LucaORCID, Liodakis IoannisORCID, Maldera SimoneORCID, Manfreda AlbertoORCID, Marin FrédéricORCID, Marscher Alan P.ORCID, Massaro FrancescoORCID, Matt GiorgioORCID, Mitsuishi Ikuyuki, Mizuno TsunefumiORCID, Negro MichelaORCID, Ng Chi-YungORCID, O’Dell Stephen L.ORCID, Omodei NicolaORCID, Oppedisano ChiaraORCID, Pavlov George G.ORCID, Peirson Abel L.ORCID, Perri MatteoORCID, Pesce-Rollins MelissaORCID, Petrucci Pierre-OlivierORCID, Possenti AndreaORCID, Puccetti SimonettaORCID, Ramsey Brian D.ORCID, Ratheesh AjayORCID, Roberts Oliver J.ORCID, Romani Roger W.ORCID, Sgrò CarmeloORCID, Slane PatrickORCID, Soffitta PaoloORCID, Spandre GloriaORCID, Swartz Douglas A.ORCID, Tamagawa ToruORCID, Tavecchio FabrizioORCID, Taverna RobertoORCID, Tawara Yuzuru, Thomas Nicholas E.ORCID, Tombesi FrancescoORCID, Trois AlessioORCID, Turolla RobertoORCID, Vink JaccoORCID, Xie FeiORCID
Abstract
Abstract
Cir X-1 is a neutron star X-ray binary characterized by strong variations in flux during its eccentric ∼16.6 day orbit. There are also strong variations in the spectral state, and it has historically shown both atoll and Z state properties. We observed the source with the Imaging X-ray Polarimetry Explorer during two orbital segments, 6 days apart, for a total of 263 ks. We find an X-ray polarization degree in these segments of 1.6% ± 0.3% and 1.4% ± 0.3% at polarization angles of 37° ± 5° and −12° ± 7°, respectively. Thus, we observed a rotation of the polarization angle by 49° ± 8° along the orbit. Because variations of accretion flow, and then of the hardness ratio, are expected during the orbit, we also studied the polarization binned in hardness ratio and found the polarization angle differing by 67° ± 11° between the lowest and highest values of the hardness ratio. We discuss possible interpretations of this result that could indicate a possible misalignment between the symmetry axes of the accretion disk and the Comptonizing region caused by the misalignment of the neutron star’s angular momentum with respect to the orbital one.
Funder
Agenzia Spaziale Italiana MOST ∣ National Key Research and Development Program of China Academy of Finland German Academic Exchange Service Ministero dell'Università e della Ricerca MOST ∣ National Natural Science Foundation of China
Publisher
American Astronomical Society
Subject
Space and Planetary Science,Astronomy and Astrophysics
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