article published yes Victor Doroshenko author Juri Poutanen author Jeremy Heyl author Sergey S. Tsygankov author Ilaria Caiazzo author 8ae5b6e7-2a03-11ee-914d-b58ed7a3b47d0000-0002-4770-5388 Roberto Turolla author Alexandra Veledina author Martin C. Weisskopf author Sofia V. Forsblom author Denis González-Caniulef author Vladislav Loktev author Christian Malacaria author Alexander A. Mushtukov author Valery F. Suleimanov author Alexander A. Lutovinov author Ilya A. Mereminskiy author Sergey V. Molkov author Alexander Salganik author Andrea Santangelo author Andrei V. Berdyugin author Vadim Kravtsov author Anagha P. Nitindala author Iván Agudo author Lucio A. Antonelli author Matteo Bachetti author Luca Baldini author Wayne H. Baumgartner author Ronaldo Bellazzini author Stefano Bianchi author Stephen D. Bongiorno author Raffaella Bonino author Alessandro Brez author Niccolò Bucciantini author Fiamma Capitanio author Simone Castellano author Elisabetta Cavazzuti author Chien-Ting Chen author Stefano Ciprini author Enrico Costa author Alessandra De Rosa author Ettore Del Monte author Laura Di Gesu author Niccolò Di Lalla author Alessandro Di Marco author Immacolata Donnarumma author Michal Dovčiak author Steven R. Ehlert author Teruaki Enoto author Yuri Evangelista author Sergio Fabiani author Riccardo Ferrazzoli author Javier A. García author Shuichi Gunji author Kiyoshi Hayashida author Wataru Iwakiri author Svetlana G. Jorstad author Philip Kaaret author Vladimir Karas author Fabian Kislat author Takao Kitaguchi author Jeffery J. Kolodziejczak author Henric Krawczynski author Fabio La Monaca author Luca Latronico author Ioannis Liodakis author Simone Maldera author Alberto Manfreda author Frédéric Marin author Andrea Marinucci author Alan P. Marscher author Herman L. Marshall author Francesco Massaro author Giorgio Matt author Ikuyuki Mitsuishi author Tsunefumi Mizuno author Fabio Muleri author Michela Negro author Chi-Yung Ng author Stephen L. O’Dell author Nicola Omodei author Chiara Oppedisano author Alessandro Papitto author George G. Pavlov author Abel L. Peirson author Matteo Perri author Melissa Pesce-Rollins author Pierre-Olivier Petrucci author Maura Pilia author Andrea Possenti author Simonetta Puccetti author Brian D. Ramsey author John Rankin author Ajay Ratheesh author Oliver J. Roberts author Roger W. Romani author Carmelo Sgrò author Patrick Slane author Paolo Soffitta author Gloria Spandre author Douglas A. Swartz author Toru Tamagawa author Fabrizio Tavecchio author Roberto Taverna author Yuzuru Tawara author Allyn F. Tennant author Nicholas E. Thomas author Francesco Tombesi author Alessio Trois author Jacco Vink author Kinwah Wu author Fei Xie author Silvia Zane author We report on Imaging X-ray polarimetry explorer (IXPE) observations of the Be-transient X-ray pulsar LS V +44 17/RX J0440.9+4431 made at two luminosity levels during the giant outburst in January–February 2023. Considering the observed spectral variability and changes in the pulse profiles, the source was likely caught in supercritical and subcritical states with significantly different emission-region geometry, associated with the presence of accretion columns and hot spots, respectively. We focus here on the pulse-phase-resolved polarimetric analysis and find that the observed dependencies of the polarization degree and polarization angle (PA) on the pulse phase are indeed drastically different for the two observations. The observed differences, if interpreted within the framework of the rotating vector model (RVM), imply dramatic variations in the spin axis inclination, the position angle, and the magnetic colatitude by tens of degrees within the space of just a few days. We suggest that the apparent changes in the observed PA phase dependence are predominantly related to the presence of an unpulsed polarized component in addition to the polarized radiation associated with the pulsar itself. We then show that the observed PA phase dependence in both observations can be explained with a single set of RVM parameters defining the pulsar’s geometry. We also suggest that the additional polarized component is likely produced by scattering of the pulsar radiation in the equatorial disk wind. EDP Sciences2023 eng Space and Planetary ScienceAstronomy and Astrophysics 0004-6361 1432-0746 2306.0211610.1051/0004-6361/202347088 677 yes Doroshenko, Victor, Juri Poutanen, Jeremy Heyl, Sergey S. Tsygankov, Ilaria Caiazzo, Roberto Turolla, Alexandra Veledina, et al. “Complex Variations in X-Ray Polarization in the X-Ray Pulsar LS V +44 17/RX J0440.9+4431.” <i>Astronomy &#38; Astrophysics</i>. EDP Sciences, 2023. <a href="https://doi.org/10.1051/0004-6361/202347088">https://doi.org/10.1051/0004-6361/202347088</a>. V. Doroshenko, J. Poutanen, J. Heyl, S.S. Tsygankov, I. Caiazzo, R. Turolla, A. Veledina, M.C. Weisskopf, S.V. Forsblom, D. González-Caniulef, V. Loktev, C. Malacaria, A.A. Mushtukov, V.F. Suleimanov, A.A. Lutovinov, I.A. Mereminskiy, S.V. Molkov, A. Salganik, A. Santangelo, A.V. Berdyugin, V. Kravtsov, A.P. Nitindala, I. Agudo, L.A. Antonelli, M. Bachetti, L. Baldini, W.H. Baumgartner, R. Bellazzini, S. Bianchi, S.D. Bongiorno, R. Bonino, A. Brez, N. Bucciantini, F. Capitanio, S. Castellano, E. Cavazzuti, C.-T. Chen, S. Ciprini, E. Costa, A. De Rosa, E. Del Monte, L. Di Gesu, N. Di Lalla, A. Di Marco, I. Donnarumma, M. Dovčiak, S.R. Ehlert, T. Enoto, Y. Evangelista, S. Fabiani, R. Ferrazzoli, J.A. García, S. Gunji, K. Hayashida, W. Iwakiri, S.G. Jorstad, P. Kaaret, V. Karas, F. Kislat, T. Kitaguchi, J.J. Kolodziejczak, H. Krawczynski, F. La Monaca, L. Latronico, I. Liodakis, S. Maldera, A. Manfreda, F. Marin, A. Marinucci, A.P. Marscher, H.L. Marshall, F. Massaro, G. Matt, I. Mitsuishi, T. Mizuno, F. Muleri, M. Negro, C.-Y. Ng, S.L. O’Dell, N. Omodei, C. Oppedisano, A. Papitto, G.G. Pavlov, A.L. Peirson, M. Perri, M. Pesce-Rollins, P.-O. Petrucci, M. Pilia, A. Possenti, S. Puccetti, B.D. Ramsey, J. Rankin, A. Ratheesh, O.J. Roberts, R.W. Romani, C. Sgrò, P. Slane, P. Soffitta, G. Spandre, D.A. Swartz, T. Tamagawa, F. Tavecchio, R. Taverna, Y. Tawara, A.F. Tennant, N.E. Thomas, F. Tombesi, A. Trois, J. Vink, K. Wu, F. Xie, S. Zane, Astronomy &#38; Astrophysics 677 (2023). Doroshenko V et al. 2023. Complex variations in X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431. Astronomy &#38; Astrophysics. 677, A57. Doroshenko, V., Poutanen, J., Heyl, J., Tsygankov, S. S., Caiazzo, I., Turolla, R., … Zane, S. (2023). Complex variations in X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431. <i>Astronomy &#38; Astrophysics</i>. EDP Sciences. <a href="https://doi.org/10.1051/0004-6361/202347088">https://doi.org/10.1051/0004-6361/202347088</a> V. Doroshenko <i>et al.</i>, “Complex variations in X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431,” <i>Astronomy &#38; Astrophysics</i>, vol. 677. EDP Sciences, 2023. Doroshenko, Victor, et al. “Complex Variations in X-Ray Polarization in the X-Ray Pulsar LS V +44 17/RX J0440.9+4431.” <i>Astronomy &#38; Astrophysics</i>, vol. 677, A57, EDP Sciences, 2023, doi:<a href="https://doi.org/10.1051/0004-6361/202347088">10.1051/0004-6361/202347088</a>. Doroshenko V, Poutanen J, Heyl J, et al. Complex variations in X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431. <i>Astronomy &#38; Astrophysics</i>. 2023;677. doi:<a href="https://doi.org/10.1051/0004-6361/202347088">10.1051/0004-6361/202347088</a> 151932024-03-26T09:46:01Z2024-04-02T06:57:11Z