Discovery of a variable energy-dependent X-ray polarization in the accreting neutron star GX 5−1

DOI: 
10.1051/0004-6361/202347374
Publication date: 
11/04/2024
Main author: 
Fabiani, Sergio
IAA authors: 
Agudo, Iván
Authors: 
Fabiani, Sergio;Capitanio, Fiamma;Iaria, Rosario;Poutanen, Juri;Gnarini, Andrea;Ursini, Francesco;Farinelli, Ruben;Bobrikova, Anna;Steiner, James F.;Svoboda, Jiri;Anitra, Alessio;Baglio, Maria C.;Carotenuto, Francesco;Del Santo, Melania;Ferrigno, Carlo;Lewis, Fraser;Russell, David M.;Russell, Thomas D.;van den Eijnden, Jakob;Cocchi, Massimo;Di Marco, Alessandro;La Monaca, Fabio;Liu, Kuan;Rankin, John;Weisskopf, Martin C.;Xie, Fei;Bianchi, Stefano;Burderi, Luciano;Di Salvo, Tiziana;Egron, Elise;Illiano, Giulia;Kaaret, Philip;Matt, Giorgio;Mikušincová, Romana;Muleri, Fabio;Papitto, Alessandro;Agudo, Iván;Antonelli, Lucio A.;Bachetti, Matteo;Baldini, Luca;Baumgartner, Wayne H.;Bellazzini, Ronaldo;Bongiorno, Stephen D.;Bonino, Raffaella;Brez, Alessandro;Bucciantini, Niccolò;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;Doroshenko, Victor;Dovčiak, 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;Kislat, Fabian;Kitaguchi, Takao;Kolodziejczak, Jeffery J.;Krawczynski, Henric;Latronico, Luca;Liodakis, Ioannis;Maldera, Simone;Manfreda, Alberto;Marin, Frédéric;Marinucci, Andrea;Marscher, Alan P.;Marshall, Herman L.;Massaro, Francesco;Mitsuishi, Ikuyuki;Mizuno, Tsunefumi;Negro, Michela;Ng, Chi-Yung;O'Dell, Stephen L.;Omodei, Nicola;Oppedisano, Chiara;Pavlov, George G.;Peirson, Abel L.;Perri, Matteo;Pesce-Rollins, Melissa;Petrucci, Pierre-Olivier;Pilia, Maura;Possenti, Andrea;Puccetti, Simonetta;Ramsey, Brian D.;Ratheesh, Ajay;Roberts, Oliver J.;Romani, Roger W.;Sgrò, Carmelo;Slane, Patrick;Soffitta, Paolo;Spandre, Gloria;Swartz, Douglas A.;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;Wu, Kinwah;Zane, Silvia
Journal: 
Astronomy and Astrophysics
Publication type: 
Article
Volume: 
684
Pages: 
A137
Abstract: 
We report on the coordinated observations of the neutron star low-mass X-ray binary (NS-LMXB) GX 5−1 in X-rays (IXPE, NICER, NuSTAR, and INTEGRAL), optical (REM and LCO), near-infrared (REM), mid-infrared (VLT VISIR), and radio (ATCA). This Z-source was observed by IXPE twice in March-April 2023 (Obs. 1 and 2). In the radio band the source was detected, but only upper limits to the linear polarization were obtained at a 3σ level of 6.1% at 5.5 GHz and 5.9% at 9 GHz in Obs. 1 and 12.5% at 5.5 GHz and 20% at 9 GHz in Obs. 2. The mid-IR, near-IR, and optical observations suggest the presence of a compact jet that peaks in the mid- or far-IR. The X-ray polarization degree was found to be 3.7%±0.4% (at 90% confidence level) during Obs. 1 when the source was in the horizontal branch of the Z-track and 1.8%±0.4% during Obs. 2 when the source was in the normal-flaring branch. These results confirm the variation in polarization degree as a function of the position of the source in the color-color diagram, as for previously observed Z-track sources (Cyg X-2 and XTE 1701−462). Evidence of a variation in the polarization angle of ∼20° with energy is found in both observations, likely related to the different, nonorthogonal polarization angles of the disk and Comptonization components, which peak at different energies.
Database: 
ADS
SCOPUS
URL: 
https://ui.adsabs.harvard.edu/#abs/2024A&A...684A.137F/abstract
ADS Bibcode: 
2024A&A...684A.137F
Keywords: 
accretion;accretion disks;stars: neutron;X-rays: binaries;X-rays: general;X-rays: individuals: GX 5−1;Astrophysics - High Energy Astrophysical Phenomena