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

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
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

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
Katso/Avaa
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EDP SCIENCES S A
doi:10.1051/0004-6361/202346541
URI
https://doi.org/10.1051/0004-6361/202346541
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Julkaisun pysyvä osoite on:
https://urn.fi/URN:NBN:fi-fe2025082789413
Tiivistelmä
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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