IXPE Observations of the Quintessential Wind-accreting X-Ray Pulsar Vela X-1

Sofia V. Forsblom , Juri Poutanen , Sergey S. Tsygankov , Matteo Bachetti , Alessandro Di Marco , Victor Doroshenko , Jeremy Heyl , Fabio La Monaca , Christian Malacaria , Herman L. Marshall , Fabio Muleri , Alexander A. Mushtukov , Maura Pilia , Daniele Rogantini , Valery F. Suleimanov , Roberto Taverna , Fei Xie , 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 , Chien-Ting Chen , Stefano Ciprini , Enrico Costa , Alessandra de Rosa , Ettore del Monte , Laura Di Gesu , Niccolò Di Lalla , Immacolata Donnarumma , 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 , Philip Kaaret , Vladimir Karas , Takao Kitaguchi , Jeffery J. Kolodziejczak , Henric Krawczynski , Luca Latronico , Ioannis Liodakis , Simone Maldera , Alberto Manfreda , Frédéric Marin (1) , Andrea Marinucci , Alan P. Marscher , Giorgio Matt , Ikuyuki Mitsuishi , Tsunefumi Mizuno , Michela Negro , Chi-Yung Ng , Stephen L. O'Dell , Nicola Omodei , Chiara Oppedisano , Alessandro Papitto , George G. Pavlov , Abel L. Peirson , Matteo Perri , Melissa Pesce-Rollins , Pierre-Olivier Petrucci (2) , Andrea Possenti , Simonetta Puccetti , Brian D. Ramsey , John Rankin , Ajay Ratheesh , Oliver J. Roberts , Roger W. Romani , Carmelo Sgrò , Patrick Slane , Paolo Soffitta , Gloria Spandre , Rashid A. Sunyaev , Douglas A. Swartz , Toru Tamagawa , Fabrizio Tavecchio , Yuzuru Tawara , Allyn F. Tennant , Nicholas E. Thomas , Francesco Tombesi , Alessio Trois , Roberto Turolla , Jacco Vink , Martin C. Weisskopf , Kinwah Wu , Silvia Zane

1 ObAS - Observatoire astronomique de Strasbourg
2 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble

The radiation from accreting X-ray pulsars was expected to be highly polarized, with some estimates for the polarization degree of up to 80%. However, phase-resolved and energy-resolved polarimetry of X-ray pulsars is required in order to test different models and to shed light on the emission processes and the geometry of the emission region. Here we present the first results of the observations of the accreting X-ray pulsar Vela X-1 performed with the Imaging X-ray Polarimetry Explorer. Vela X-1 is considered to be the archetypal example of a wind-accreting, high-mass X-ray binary system, consisting of a highly magnetized neutron star accreting matter from its supergiant stellar companion. The spectropolarimetric analysis of the phase-averaged data for Vela X-1 reveals a polarization degree (PD) of 2.3% ± 0.4% at the polarization angle (PA) of -47.°3 ± 5.°4. A low PD is consistent with the results obtained for other X-ray pulsars and is likely related to the inverse temperature structure of the neutron star atmosphere. The energy-resolved analysis shows the PD above 5 keV reaching 6%-10% and a ~90° difference in the PA compared to the data in the 2-3 keV range. The phase-resolved spectropolarimetric analysis finds a PD in the range 0%-9% with the PA varying between -80° and 40°.

Keywords: Pulsars; Starlight polarization; Neutron stars; High mass x-ray binary stars; Magnetic fields; Accretion

Domains: Sciences of the Universe [physics]

Sofia V. Forsblom, Juri Poutanen, Sergey S. Tsygankov, Matteo Bachetti, Alessandro Di Marco, et al.. IXPE Observations of the Quintessential Wind-accreting X-Ray Pulsar Vela X-1. The Astrophysical Journal Letters, 2023, 947, ⟨10.3847/2041-8213/acc391⟩. ⟨insu-04079451⟩