Discovery of a variable energy-dependent X-ray polarization in the accreting neutron star GX 5-1
- Authors: Fabiani S.; Capitanio F.; Iaria R.; Gnarini A.; Ursini F.; Farinelli R.; Bobrikova A.; Steiner J.F.; Svoboda J.; Anitra A.; Baglio M.C.; Carotenuto F.; Santo M.D.; Ferrigno C.; Lewis F.; Russell D.M.; Russell T.D.; Van Den Eijnden J.; Cocchi M.; Marco A.D.; Monaca F.L.; Rankin J.; Weisskopf M.C.; Xie F.; Bianchi S.; Burderi L.; Di Salvo T.; Egron E.; Illiano G.; Kaaret P.; Matt G.; Mikusincova R.; Muleri F.; Papitto A.; Agudo I.; Antonelli L.A.; Bachetti M.; Baldini L.; Baumgartner W.H.; Bellazzini R.; Bongiorno S.D.; Bonino R.; Brez A.; Bucciantini N.; Castellano S.; Cavazzuti E.; Chen C.-T.; Ciprini S.; Costa E.; De Rosa A.; Del Monte E.; Di Gesu L.; Di Lalla N.; Donnarumma I.; Doroshenko V.; Dovciak M.; Ehlert S.R.; Enoto T.; Evangelista Y.; Ferrazzoli R.; Garcia J.A.; Gunji S.; Hayashida K.; Heyl J.; Iwakiri W.; Jorstad S.G.; Karas V.; Kislat F.; Kolodziejczak J.J.; Krawczynski H.; Latronico L.; Liodakis I.; Maldera S.; Manfreda A.; Marin F.; Marinucci A.; Marscher A.P.; Marshall H.L.; Massaro F.; Mitsuishi I.; Mizuno T.; Negro M.; Ng C.-Y.; O'Dell S.L.; Omodei N.; Oppedisano C.; Pavlov G.G.; Peirson A.L.; Perri M.; Pesce-Rollins M.; Petrucci P.-O.; Pilia M.; Possenti A.; Puccetti S.; Ramsey B.D.; Ratheesh A.; Roberts O.J.; Romani R.W.; Sgro C.; Slane P.; Soffitta P.; Spandre G.; Swartz D.A.; Tamagawa T.; Tavecchio F.; Taverna R.; Tennant A.F.; Thomas N.E.; Tombesi F.; Trois A.; Tsygankov S.S.; Turolla R.; Vink J.; Wu K.; Zane S.; Poutanen J.; Liu K.; Tawara Y.; Kitaguchi T.
- Publication year: 2024
- Type: Articolo in rivista
- OA Link: http://hdl.handle.net/10447/636314
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.