Observations of 4U 1626–67 with the Imaging X-Ray Polarimetry Explorer

Herman Marshall , Mason Ng , Daniele Rogantini , Jeremy Heyl , Sergey Tsygankov , Juri Poutanen , Enrico Costa , Silvia Zane , Christian Malacaria , Iván Agudo , Lucio Antonelli , Matteo Bachetti , Luca Baldini , Wayne Baumgartner , Ronaldo Bellazzini , Stefano Bianchi , Stephen 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 , Alessandro Di Marco , Immacolata Donnarumma , Victor Doroshenko , Michal Dovčiak , Steven Ehlert , Teruaki Enoto , Yuri Evangelista , Sergio Fabiani , Riccardo Ferrazzoli , Javier Garcia , Shuichi Gunji , Kiyoshi Hayashida , Wataru Iwakiri , Svetlana Jorstad , Vladimir Karas , Takao Kitaguchi , Jeffery Kolodziejczak , Henric Krawczynski , Fabio La Monaca , Luca Latronico , Ioannis Liodakis , Simone Maldera , Alberto Manfreda , Frédéric Marin (1) , Andrea Marinucci , Alan Marscher , Giorgio Matt , Ikuyuki Mitsuishi , Tsunefumi Mizuno , Fabio Muleri , C.-Y. Ng , Stephen O’dell , Nicola Omodei , Chiara Oppedisano , Alessandro Papitto , George Pavlov , Abel Peirson , Matteo Perri , Melissa Pesce-Rollins , Pierre-Olivier Petrucci , Maura Pilia , Andrea Possenti , Simonetta Puccetti , Brian Ramsey , John Rankin , Ajay Ratheesh , Roger Romani , Carmelo Sgrò , Patrick Slane , Paolo Soffitta , Gloria Spandre , Toru Tamagawa , Fabrizio Tavecchio , Roberto Taverna , Yuzuru Tawara , Allyn Tennant , Nicholas Thomas , Francesco Tombesi , Alessio Trois , Roberto Turolla , Jacco Vink , Martin Weisskopf , Kinwah Wu , Fei Xie , Norbert Schulz , Deepto Chakrabarty

1 ObAS - Observatoire astronomique de Strasbourg

Abstract We present measurements of the polarization of X-rays in the 2–8 keV band from the pulsar in the ultracompact low-mass X-ray binary 4U 1626–67 using data from the Imaging X-Ray Polarimetry Explorer (IXPE). The 7.66 s pulsations were clearly detected throughout the IXPE observations as well as in the NICER soft X-ray observations, which we used as the basis for our timing analysis and to constrain the spectral shape over the 0.4–10 keV energy band. Chandra HETGS high-resolution X-ray spectra were also obtained near the times of the IXPE observations for firm spectral modeling. We found an upper limit on the pulse-averaged linear polarization of <4% (at 95% confidence). Similarly, there was no significant detection of polarized flux in pulse phase intervals when subdividing the bandpass by energy. However, spectropolarimetric modeling over the full bandpass in pulse phase intervals provided a marginal detection of polarization of the power-law spectral component at the 4.8% ± 2.3% level (90% confidence). We discuss the implications concerning the accretion geometry onto the pulsar, favoring two-component models of the pulsed emission.

Domaines: Planète et Univers [physics]; Astrophysique [astro-ph]

Herman Marshall, Mason Ng, Daniele Rogantini, Jeremy Heyl, Sergey Tsygankov, et al.. Observations of 4U 1626–67 with the Imaging X-Ray Polarimetry Explorer. The Astrophysical Journal, 2022, 940 (1), pp.70. ⟨10.3847/1538-4357/ac98c2⟩. ⟨insu-03875817⟩