A1 Refereed original research article in a scientific journal
X-ray polarimetry and spectroscopy of the neutron star low-mass X-ray binary GX 9+9: An in-depth study with IXPE and NuSTAR
Authors: Ursini F, Farinelli R, Gnarini A, Poutanen J, Bianchi S, Capitanio F, Di Marco A, Fabiani S, La Monaca F, Malacaria C, Matt G, Mikusincova R, Cocchi M, Kaaret P, Kajava JJE, Pilia M, Zhang W, Agudo I, Antonelli LA, Bachetti M, Baldini L, Baumgartner WH, Bellazzini R, Bongiorno SD, Bonino R, Brez A, Bucciantini N, Castellano S, Cavazzuti E, Chen CT, Ciprini S, Costa E, De Rosa A, Del Monte E, Di Gesu L, Di Lalla N, Donnarumma I, Doroshenko V, Dovciak M, Ehlert SR, Enoto T, Evangelista Y, Ferrazzoli R, Garcia JA, Gunji S, Hayashida K, Heyl J, Iwakiri W, Jorstad SG, Karas V, Kislat F, Kitaguchi T, Kolodziejczak JJ, Krawczynski H, Latronico L, Liodakis I, Maldera S, Manfreda A, Marin F, Marinucci A, Marscher AP, Marshall HL, Massaro F, Mitsuishi I, Mizuno T, Muleri F, Negro M, Ng CY, O'Dell SL, Omodei N, Oppedisano C, Papitto A, Pavlov GG, Peirson AL, Perri M, Pesce-Rollins M, Petrucci PO, Pilia M, Possenti A, Puccetti S, Ramsey BD, Rankin J, Ratheesh A, Roberts OJ, Romani RW, Sgro C, Slane P, Soffitta P, Spandre G, Swartz DA, Tamagawa T, Tavecchio F, Taverna R, Tawara Y, Tennant AF, Thomas NE, Tombesi F, Trois A, Tsygankov SS, Turolla R, Vink J, Weisskopf MC, Wu K, Xie F, Zane S
Publisher: EDP SCIENCES S A
Publication year: 2023
Journal: Astronomy and Astrophysics
Journal name in source: ASTRONOMY & ASTROPHYSICS
Journal acronym: ASTRON ASTROPHYS
Article number: A20
Volume: 676
Number of pages: 10
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202346541
Web address : https://doi.org/10.1051/0004-6361/202346541
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/180691513
We report on a comprehensive analysis of simultaneous X-ray polarimetric and spectral data of the bright atoll source GX 9+9 with the Imaging X-ray Polarimetry Explorer (IXPE) and NuSTAR. The source is significantly polarized in the 4-8 keV band, with a degree of 2.2% & PLUSMN; 0.5% (uncertainty at the 68% confidence level). The NuSTAR broad-band spectrum clearly shows an iron line, and is well described by a model including thermal disc emission, a Comptonized component, and reflection. From a spectro-polarimetric fit, we obtain an upper limit to the polarization degree of the disc of 4% (at the 99% confidence level), while the contribution of Comptonized and reflected radiation cannot be conclusively separated. However, the polarization is consistent with resulting from a combination of Comptonization in a boundary or spreading layer, plus reflection off the disc, which significantly contributes in any realistic scenario.
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