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
Journal
Date Issued
2023
Author(s)
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Gnarini, A.
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Poutanen, J.
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BIANCHI, Simone
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Malacaria, C.
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Matt, G.
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Thomas, N. E.
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Tsygankov, S. S.
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Turolla, R.
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Vink, J.
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Weisskopf, M. C.
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Wu, K.
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Zane, S.
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Mikušincová, R.
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Kaaret, P.
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Kajava, J. J. E.
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Zhang, W.
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Agudo, I.
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Baldini, L.
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Baumgartner, W. H.
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Bellazzini, R.
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Bongiorno, S. D.
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Bonino, R.
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Brez, A.
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Castellano, S.
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Cavazzuti, E.
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Chen, C.-T.
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Ciprini, S.
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Di Gesu, L.
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Di Lalla, N.
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Donnarumma, I.
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Doroshenko, V.
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Dovčiak, M.
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Ehlert, S. R.
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Enoto, T.
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Ferrazzoli, R.
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Garcia, J. A.
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Gunji, S.
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Hayashida, K.
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Heyl, J.
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Iwakiri, W.
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Jorstad, S. G.
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Karas, V.
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Kislat, F.
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Kitaguchi, T.
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Kolodziejczak, J. J.
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Krawczynski, H.
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Latronico, L.
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Liodakis, I.
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Maldera, S.
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Manfreda, A.
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Marin, F.
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Marinucci, A.
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Marscher, A. P.
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Marshall, H. L.
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Mitsuishi, I.
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Mizuno, T.
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Negro, M.
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Ng, C.-Y.
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O’Dell, S. L.
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Omodei, N.
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Oppedisano, C.
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Pavlov, G. G.
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Peirson, A. L.
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Pesce-Rollins, M.
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Petrucci, P.-O.
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Puccetti, S.
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Ramsey, B. D.
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Rankin, J.
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Ratheesh, A.
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Roberts, O. J.
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Romani, R. W.
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Sgrò, C.
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Slane, P.
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Spandre, G.
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Swartz, D. A.
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Tamagawa, T.
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Taverna, R.
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Tawara, Y.
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Tennant, A. F.
Abstract
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% ± 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.
Volume
676
Start page
A20
Issn Identifier
0004-6361
Ads BibCode
2023A&A...676A..20U
Rights
open.access
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