@article{discovery10186249, title = {X-Ray Polarized View of the Accretion Geometry in the X-Ray Binary Circinus X-1}, journal = {Astrophysical Journal Letters}, year = {2024}, publisher = {American Astronomical Society}, note = {Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.}, volume = {961}, number = {1}, month = {January}, abstract = {Cir X-1 is a neutron star X-ray binary characterized by strong variations in flux during its eccentric {$\sim$}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\% {$\pm$} 0.3\% and 1.4\% {$\pm$} 0.3\% at polarization angles of 37o {$\pm$} 5o and ?12o {$\pm$} 7o, respectively. Thus, we observed a rotation of the polarization angle by 49o {$\pm$} 8o 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 67o {$\pm$} 11o 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.}, issn = {2041-8205}, url = {https://doi.org/10.3847/2041-8213/ad1832}, author = {Rankin, J and La Monaca, F and Di Marco, A and Poutanen, J and Bobrikova, A and Kravtsov, V and Muleri, F and Pilia, M and Veledina, A and Fender, R and Kaaret, P and Kim, DE and Marinucci, A and Marshall, HL and Papitto, A and Tennant, AF and Tsygankov, SS and Weisskopf, MC and Wu, K and Zane, S and Ambrosino, F and Farinelli, R and Gnarini, A and Agudo, I and Antonelli, LA and Bachetti, M and Baldini, L and Baumgartner, WH and Bellazzini, R and Bianchi, S and Bongiorno, SD and Bonino, R and Brez, A and Bucciantini, N and Capitanio, F and Castellano, S and Cavazzuti, E and Chen, CT and Ciprini, S and Costa, E and De Rosa, A and Del Monte, E and Di Gesu, L and Di Lalla, N and Donnarumma, I and Doroshenko, V and Dov{\vc}iak, M and Ehlert, SR and Enoto, T and Evangelista, Y and Fabiani, S and Ferrazzoli, R and Garcia, JA and Gunji, S and Hayashida, K and Heyl, J and Iwakiri, W and Jorstad, SG and Karas, V and Kislat, F and Kitaguchi, T and Kolodziejczak, JJ and Krawczynski, H and Latronico, L and Liodakis, I and Maldera, S and Manfreda, A and Marin, F and Marscher, AP and Massaro, F and Matt, G and Mitsuishi, I and Mizuno, T and Negro, M and Ng, CY and O'Dell, SL and Omodei, N and Oppedisano, C and Pavlov, GG and Peirson, AL and Perri, M and Pesce-Rollins, M and Petrucci, PO and Possenti, A and Puccetti, S and Ramsey, BD and Ratheesh, A and Roberts, OJ and Romani, RW and Sgr{\`o}, C and Slane, P and Soffitta, P and Spandre, G and Swartz, DA and Tamagawa, T and Tavecchio, F and Taverna, R and Tawara, Y and Thomas, NE and Tombesi, F} }