Polarization properties of the weakly magnetized neutron star X-ray binary GS 1826-238 in the high soft state
Capitanio, Fiamma; Fabiani, Sergio; Gnarini, Andrea; Ursini, Francesco; Ferrigno, Carlo; Matt, Giorgio; Poutanen, Juri; Cocchi, Massimo; Mikusincova, Romana; Farinelli, Ruben; Bianchi, Stefano; Kajava, Jari J.E.; Muleri, Fabio; Sanchez-Fernandez, Celia; Soffitta, Paolo; Wu, Kinwah; Agudo, Ivan; Antonelli, Lucio A.; Bachetti, Matteo; Baldini, Luca; Baumgartner, Wayne H.; Bellazzini, Ronaldo; Bongiorno, Stephen D.; Bonino, Raffaella; Brez, Alessandro; Bucciantini, Niccoló; Castellano, Simone; Cavazzuti, Elisabetta; Ciprini, Stefano; Costa, Enrico; Rosa, Alessandra De; Monte, Ettore Del; Gesu, Laura Di; Lalla, Niccolo Di; Marco, Alessandro Di; Donnarumma, Immacolata; Doroshenko, Victor; Dovciak, Michal; Ehlert, Steven R.; Enoto, Teruaki; Evangelista, Yuri; Ferrazzoli, Riccardo; Garcia, Javier A.; Gunji, Shuichi; Hayashida, Kiyoshi; Heyl, Jeremy; Iwakiri, Wataru; Jorstad, Svetlana G.; Karas, Vladimir; Kitaguchi, Takao; Kolodziejczak, Jeffery J.; Krawczynski, Henric; Monaca, Fabio La; Latronico, Luca; Liodakis, Ioannis; Maldera, Simone; Manfreda, Alberto; Marin, Fréedèric; Marinucci, Andrea; Marscher, Alan P.; Marshall, Herman L.; Mitsuishi, Ikuyuki; Mizuno, Tsunefumi; Ng, C.-Y.; 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; Romani, Roger W.; Sgrò, Carmelo; Slane, Patrick; Spandre, Gloria; Tamagawa, Toru; Tavecchio, Fabrizio; Taverna, Roberto; Tawara, Yuzuru; Tennant, Allyn F.; Thomas, Nicholas E.; Tombesi, Francesco; Trois, Alessio; Tsygankov, Sergey S.; Turolla, Roberto; Vink, Jacco; Weisskopf, Martin C.; Xie, Fei; Zane, Silvia
The launch of the Imaging X-ray Polarimetry Explorer (IXPE) on 2021 December
9 has opened a new window in X-ray astronomy. We report here the results of the
first IXPE observation of a weakly magnetized neutron star, GS 1826-238,
performed on 2022 March 29-31 when the source was in a high soft state. An
upper limit (99.73% confidence level) of 1.3% for the linear polarization
degree is obtained over the IXPE 2-8 keV energy range. Coordinated INTEGRAL and
NICER observations were carried out simultaneously with IXPE. The spectral
parameters obtained from the fits to the broad-band spectrum were used as
inputs for Monte Carlo simulations considering different possible geometries of
the X-ray emitting region. Comparing the IXPE upper limit with these
simulations, we can put constraints on the geometry and inclination angle of GS
1826-238.
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