2026-04-13T02:00:18Zhttps://recercat.cat/oai/request
oai:recercat.cat:2117/4390242026-03-20T03:49:01Zcom_2072_1033col_2072_452950
RECERCAT author Mastroserio, Guglielmo author Marco, Barbara de author Baglio, Maria Cristina author Carotenuto, Francesco author Fabiani, Sergio author Russell, Thomas author Capitanio, Fiamma author Cavecchi, Yuri author Motta, Silvia author Russell, David author Dovciak, Michal 2025-01-10 We present the first X-ray polarization measurements of GX 339–4. IXPE observed this source twice during its 2023–2024 outburst, once in the soft-intermediate state and again during a soft state. The observation taken during the intermediate state shows a significant (4s) polarization degree PX = 1.3% ± 0.3% and polarization angle ¿X = -74° ± 7° only in the 3–8 keV band. FORS2 at the Very Large Telescope observed the source simultaneously, detecting optical polarization in the B, V, R, and I bands (between ~0.1% and ~0.7%), all roughly aligned with the X-ray polarization. We also detect a discrete jet knot from radio observations with the Australia Telescope Compact Array taken later in time; this knot would have been ejected from the system around the same time as the hard-to-soft X-ray state transition, and a bright radio flare occurred ~3 months earlier. The proper motion of the jet knot provides a direct measurement of the jet orientation angle on the plane of the sky at the time of the ejection. We find that both the X-ray and optical polarization angles are aligned with the direction of the ballistic jet.Peer ReviewedPostprint (published version) http://creativecommons.org/licenses/by/4.0/ Open Access Attribution 4.0 International Àrees temàtiques de la UPC::Física::Astronomia i astrofísica Accretion Low-mass x-ray binary stars X-ray astronomy Radio astronomy Astrophysical black holes X-Ray and optical polarization aligned with the radio jet ejecta in GX 339-4 Article