Complex variations of X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431
Creators: name: Doroshenko, Victor
name: Poutanen, Juri
name: Heyl, Jeremy
name: Tsygankov, Sergey S.
name: Caiazzo, Ilaria
name: Turolla, Roberto
name: Veledina, Alexandra
name: Weisskopf, Martin C.
name: Forsblom, Sofia V.
name: González-Caniulef, Denis
name: Loktev, Vladislav
name: Malacaria, Christian
name: Mushtukov, Alexander A.
name: Suleimanov, Valery F.
name: Lutovinov, Alexander A.
name: Mereminskiy, Ilya A.
name: Molkov, Sergey V.
name: Salganik, Alexander
name: Santangelo, Andrea
name: Berdyugin, Andrei V.
name: Kravtsov, Vadim
name: Nitindala, Anagha P.
name: Agudo, Iván
name: Antonelli, Lucio A.
name: Bachetti, Matteo
name: Baldini, Luca
name: Baumgartner, Wayne H.
name: Bellazzini, Ronaldo
name: Bianchi, Stefano
name: Bongiorno, Stephen D.
name: Bonino, Raffaella
name: Brez, Alessandro
name: Bucciantini, Niccolò
name: Capitanio, Fiamma
name: Castellano, Simone
name: Cavazzuti, Elisabetta
name: Chen, Chien-Ting
name: Ciprini, Stefano
name: Costa, Enrico
name: De Rosa, Alessandra
name: Del Monte, Ettore
name: Di Gesu, Laura
name: Di Lalla, Niccolò
name: Di Marco, Alessandro
name: Donnarumma, Immacolata
name: Dovčiak, Michal
name: Ehlert, Steven R.
name: Enoto, Teruaki
name: Evangelista, Yuri
name: Fabiani, Sergio
name: Ferrazzoli, Riccardo
name: García, Javier A.
name: Gunji, Shuichi
name: Hayashida, Kiyoshi
name: Iwakiri, Wataru
name: Jorstad, Svetlana G.
name: Kaaret, Philip
name: Karas, Vladimir
name: Kislat, Fabian
name: Kitaguchi, Takao
name: Kolodziejczak, Jeffery J.
name: Krawczynski, Henric
name: La Monaca, Fabio
name: Latronico, Luca
name: Liodakis, Ioannis
name: Maldera, Simone
name: Manfreda, Alberto
name: Marin, Frédéric
name: Marinucci, Andrea
name: Marscher, Alan P.
name: Marshall, Herman L.
name: Massaro, Francesco
name: Matt, Giorgio
name: Mitsuishi, Ikuyuki
name: Mizuno, Tsunefumi
name: Muleri, Fabio
name: Negro, Michela
name: Ng, Chi-Yung
name: O'Dell, Stephen L.
name: Omodei, Nicola
name: Oppedisano, Chiara
name: Papitto, Alessandro
name: Pavlov, George G.
name: Peirson, Abel L.
name: Perri, Matteo
name: Pesce-Rollins, Melissa
name: Petrucci, Pierre-Olivier
name: Pilia, Maura
name: Possenti, Andrea
name: Puccetti, Simonetta
name: Ramsey, Brian D.
name: Rankin, John
name: Ratheesh, Ajay
name: Roberts, Oliver J.
name: Romani, Roger W.
name: Sgrò, Carmelo
name: Slane, Patrick
name: Soffitta, Paolo
name: Spandre, Gloria
name: Swartz, Douglas A.
name: Tamagawa, Toru
name: Tavecchio, Fabrizio
name: Taverna, Roberto
name: Tawara, Yuzuru
name: Tennant, Allyn F.
name: Thomas, Nicholas E.
name: Tombesi, Francesco
name: Trois, Alessio
name: Vink, Jacco
name: Wu, Kinwah
name: Xie, Fei
name: Zane, Silvia
Publisher: name: arXiv
Year: 2023
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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.
description: 10 pages, 7 figures, accepted in A&amp;A