Author:
Tsygankov Sergey S.,Doroshenko Victor,Mushtukov Alexander A.,Poutanen Juri,Di Marco Alessandro,Heyl Jeremy,La Monaca Fabio,Forsblom Sofia V.,Malacaria Christian,Marshall Herman L.,Suleimanov Valery F.,Svoboda Jiri,Taverna Roberto,Ursini Francesco,Agudo Iván,Antonelli Lucio A.,Bachetti Matteo,Baldini Luca,Baumgartner Wayne H.,Bellazzini Ronaldo,Bianchi Stefano,Bongiorno Stephen D.,Bonino Raffaella,Brez Alessandro,Bucciantini Niccolò,Capitanio Fiamma,Castellano Simone,Cavazzuti Elisabetta,Chen Chien-Ting,Ciprini Stefano,Costa Enrico,De Rosa Alessandra,Del Monte Ettore,Di Gesu Laura,Di Lalla Niccolò,Donnarumma Immacolata,Dovčiak Michal,Ehlert Steven R.,Enoto Teruaki,Evangelista Yuri,Fabiani Sergio,Ferrazzoli Riccardo,Garcia Javier A.,Gunji Shuichi,Hayashida Kiyoshi,Iwakiri Wataru,Jorstad Svetlana G.,Kaaret Philip,Karas Vladimir,Kislat Fabian,Kitaguchi Takao,Kolodziejczak Jeffery J.,Krawczynski Henric,Latronico Luca,Liodakis Ioannis,Maldera Simone,Manfreda Alberto,Marin Frédéric,Marinucci Andrea,Marscher Alan P.,Massaro Francesco,Matt Giorgio,Mitsuishi Ikuyuki,Mizuno Tsunefumi,Muleri Fabio,Negro Michela,Ng Chi-Yung,O’Dell Stephen L.,Omodei Nicola,Oppedisano Chiara,Papitto Alessandro,Pavlov George G.,Peirson Abel L.,Perri Matteo,Pesce-Rollins Melissa,Petrucci Pierre-Olivier,Pilia Maura,Possenti Andrea,Puccetti Simonetta,Ramsey Brian D.,Rankin John,Ratheesh Ajay,Roberts Oliver J.,Romani Roger W.,Sgrò Carmelo,Slane Patrick,Soffitta Paolo,Spandre Gloria,Swartz Douglas A.,Tamagawa Toru,Tavecchio Fabrizio,Tawara Yuzuru,Tennant Allyn F.,Thomas Nicholas E.,Tombesi Francesco,Trois Alessio,Turolla Roberto,Vink Jacco,Weisskopf Martin C.,Wu Kinwah,Xie Fei,Zane Silvia
Abstract
X-ray polarimetry is a unique way to probe the geometrical configuration of highly magnetized accreting neutron stars (X-ray pulsars). GRO J1008−57 is the first transient X-ray pulsar observed at two different flux levels by the Imaging X-ray Polarimetry Explorer (IXPE) during its outburst in November 2022. We find the polarization properties of GRO J1008−57 to be independent of its luminosity, with the polarization degree varying between nondetection and about 15% over the pulse phase. Fitting the phase-resolved spectro-polarimetric data with the rotating vector model allowed us to estimate the pulsar inclination (130°, which is in good agreement with the orbital inclination), the position angle (75°) of the pulsar spin axis, and the magnetic obliquity (∼74°). This makes GRO J1008−57 the first confidently identified nearly orthogonal rotator among X-ray pulsars. We discuss our results in the context of the neutron star atmosphere models and theories of the axis alignment of accreting pulsars.
Subject
Space and Planetary Science,Astronomy and Astrophysics