Determination of X-ray pulsar geometry with IXPE polarimetry

• DOI: 10.1038/s41550-022-01799-5
• Publication Date: 2022-10-24T16:03:59Z
• Authors: Victor Doroshenko; Juri Poutanen; Sergey S. Tsygankov; Valery F. Suleimanov; Matteo Bachetti; Ilaria Caiazzo; Enrico Costa; Alessandro Di Marco; Jeremy Heyl; Fabio La Monaca; Fabio Muleri; Alexander A. Mush...; George G. Pavlov; Brian D. Ramsey; John Rankin; Andrea Santangelo; Paolo Soffitta; Rüdiger Staubert; Martin C. Weisskopf; Silvia Zane; Iván Agudo; Lucio A. Antonelli; Luca Baldini; Wayne H. Baumgartner; Ronaldo Bellazzini; Stefano Bianchi; Stephen D. Bongiorno; Raffaella Bonino; Alessandro Brez; Niccolò Bucciantini; Fiamma Capitanio; Simone Castellano; Elisabetta Cavazzuti; Stefano Ciprini; Alessandra De Rosa; Ettore Del Monte; Laura Di Gesu; Niccolò Di Lalla; Immacolata Donnar...; Michal Dovčiak; Steven R. Ehlert; Teruaki Enoto; Yuri Evangelista; Sergio Fabiani; Riccardo Ferrazzoli; Javier A. Garcia; Shuichi Gunji; Kiyoshi Hayashida; Wataru Iwakiri; Svetlana G. Jorstad; Vladimir Karas; Takao Kitaguchi; Jeffery J. Kolodz...; Henric Krawczynski; Luca Latronico; Ioannis Liodakis; Simone Maldera; Alberto Manfreda; Frédéric Marin; Andrea Marinucci; Alan P. Marscher; Herman L. Marshall; Giorgio Matt; Ikuyuki Mitsuishi; Tsunefumi Mizuno; Chi-Yung Ng; Stephen L. O’Dell; Nicola Omodei; Chiara Oppedisano; Alessandro Papitto; Abel L. Peirson; Matteo Perri; Melissa Pesce-Rol...; Maura Pilia; Andrea Possenti; Simonetta Puccetti; Ajay Ratheesh; Roger W. Romani; Carmelo Sgrò; Patrick Slane; Gloria Spandre; Rashid A. Sunyaev; Toru Tamagawa; Fabrizio Tavecchio; Roberto Taverna; Yuzuru Tawara; Allyn F. Tennant; Nicolas E. Thomas; Francesco Tombesi; Alessio Trois; Roberto Turolla; Jacco Vink; Kinwah Wu; Fei Xie
• Keywords: High Energy Astrophysical Phenomena (astro-ph.HE); Space sciences; FOS: Physical sciences; Astronomy and Astrophysics; Settore FIS/05 - ASTRONOMIA E ASTROFISICA; 530; 01 natural sciences; 7. Clean energy; 520; 620; [SDU] Sciences of the Universe [physics]; Particle and high energy physics; Astronomical sciences; 0103 physical sciences; Astrophysics - High Energy Astrophysical Phenomena

31 pages 7 figures, published<br/>Using observations of X-ray pulsar Her X-1 by the Imaging X-ray Polarimetry Explorer, we report on a highly significant ($>17σ$) detection of the polarization signal from an accreting neutron star. The observed degree of the linear polarization of $\sim$10\% is found to be far below theoretical expectations for this object, and stays low throughout the spin cycle of the pulsar. Both the polarization degree and the angle exhibit variability with pulse phase, which allowed us to measure the pulsar spin position angle 57(2) deg and the magnetic obliquity 12(4) deg, which is an essential step towards detailed modelling of the intrinsic emission of X-ray pulsars. Combining our results with the optical polarimetric data, we find that the spin axis of the neutron star and the angular momentum of the binary orbit are misaligned by at least $\sim$20 deg, which is a strong argument in support of the models explaining stability of the observed super-orbital variability with the precession of the neutron star.<br/>