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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2026
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| Online Access: | https://arxiv.org/abs/2603.03463 |
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| _version_ | 1866910040106991616 |
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| author | Ravi, Swati Marra, Lorenzo Steiner, James F. Mastroserio, Guglielmo Ng, Mason Neilsen, Joey Marshall, Herman L. Capitanio, Fiamma Datta, Sudeb Ranjan Egron, Elise Garcia, Javier A. Ingram, Adam Kaaret, Philip Koenig, Ole Liu, Honghui Mikusincova, Romana Nathan, Edward J. R. Petrucci, P. -O. Podgorny, Jakub Salvaggio, Chiara Svoboda, Jiri Veledina, Alexandra Zhang, Yuexin |
| author_facet | Ravi, Swati Marra, Lorenzo Steiner, James F. Mastroserio, Guglielmo Ng, Mason Neilsen, Joey Marshall, Herman L. Capitanio, Fiamma Datta, Sudeb Ranjan Egron, Elise Garcia, Javier A. Ingram, Adam Kaaret, Philip Koenig, Ole Liu, Honghui Mikusincova, Romana Nathan, Edward J. R. Petrucci, P. -O. Podgorny, Jakub Salvaggio, Chiara Svoboda, Jiri Veledina, Alexandra Zhang, Yuexin |
| contents | We report the discovery of significant X-ray polarization from the dynamically confirmed black hole X-ray binary (BHXB) GS 1354-64 during its 2025-2026 outburst, obtained with the Imaging X-ray Polarimetry Explorer (IXPE). The observation, obtained shortly after a bright X-ray flare, captures the source in an intermediate state following a stalled (failed) state transition. We discover significant 2-8 keV polarization at the ~4% level with high statistical support--14-sigma significance from frequentist analysis and log Bayes Factor 283+/-1 in a Bayesian framework--measuring PD 4.0+/-0.2% and PA-1+/-2 degrees (90% credible interval). The PD exhibits a statistically significant increasing trend with energy--the strongest such increase yet observed by IXPE in a BHXB--going from 2.1+/-0.3% in the 2-3 keV band to 11+/-3% in the 6.5-7 keV band, while the PA appears stable across both energy and time to within statistical uncertainties. Timing analysis of the IXPE data reveals a ~5 Hz Type-C quasi-periodic oscillation. IXPE + NuSTAR spectropolarimetric modeling suggests that the data can be described by polarized thermal disk and Comptonized components with PAs differing by ~90 degrees, or by a dominant Comptonized polarized component whose effective PD increases across the IXPE bandpass--the inferred component-level polarization levels are therefore model-dependent. In either picture, GS 1354-64 retains a strong coronal component during the transitional period observed by IXPE. These results illustrate how X-ray polarimetry can provide a sensitive diagnostic of the accretion state and geometry in black hole X-ray binary accretion flows, exploring a liminal phase at the cusp of state transition. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2603_03463 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Discovery of Strong Energy-Dependent X-ray Polarization in the Intermediate State of GS 1354-64 Ravi, Swati Marra, Lorenzo Steiner, James F. Mastroserio, Guglielmo Ng, Mason Neilsen, Joey Marshall, Herman L. Capitanio, Fiamma Datta, Sudeb Ranjan Egron, Elise Garcia, Javier A. Ingram, Adam Kaaret, Philip Koenig, Ole Liu, Honghui Mikusincova, Romana Nathan, Edward J. R. Petrucci, P. -O. Podgorny, Jakub Salvaggio, Chiara Svoboda, Jiri Veledina, Alexandra Zhang, Yuexin High Energy Astrophysical Phenomena We report the discovery of significant X-ray polarization from the dynamically confirmed black hole X-ray binary (BHXB) GS 1354-64 during its 2025-2026 outburst, obtained with the Imaging X-ray Polarimetry Explorer (IXPE). The observation, obtained shortly after a bright X-ray flare, captures the source in an intermediate state following a stalled (failed) state transition. We discover significant 2-8 keV polarization at the ~4% level with high statistical support--14-sigma significance from frequentist analysis and log Bayes Factor 283+/-1 in a Bayesian framework--measuring PD 4.0+/-0.2% and PA-1+/-2 degrees (90% credible interval). The PD exhibits a statistically significant increasing trend with energy--the strongest such increase yet observed by IXPE in a BHXB--going from 2.1+/-0.3% in the 2-3 keV band to 11+/-3% in the 6.5-7 keV band, while the PA appears stable across both energy and time to within statistical uncertainties. Timing analysis of the IXPE data reveals a ~5 Hz Type-C quasi-periodic oscillation. IXPE + NuSTAR spectropolarimetric modeling suggests that the data can be described by polarized thermal disk and Comptonized components with PAs differing by ~90 degrees, or by a dominant Comptonized polarized component whose effective PD increases across the IXPE bandpass--the inferred component-level polarization levels are therefore model-dependent. In either picture, GS 1354-64 retains a strong coronal component during the transitional period observed by IXPE. These results illustrate how X-ray polarimetry can provide a sensitive diagnostic of the accretion state and geometry in black hole X-ray binary accretion flows, exploring a liminal phase at the cusp of state transition. |
| title | Discovery of Strong Energy-Dependent X-ray Polarization in the Intermediate State of GS 1354-64 |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2603.03463 |