Evaluation of Several Explanations of the Strong X-Ray Polarization of the Black Hole X-Ray Binary 4U 1630-47
The Imaging X-ray Polarimetry Explorer observations of the X-ray binary 4U 1630–47 in the high soft state revealed high linear polarization degrees (PDs) rising from 6% at 2 keV to 10% at 8 keV. We discuss in this Letter three different mechanisms that impact the polarization of the observed X-rays:...
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2024-01-01
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| Online Access: | https://doi.org/10.3847/2041-8213/ad855c |
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| author | Henric Krawczynski Yajie Yuan Alexander Y. Chen Kun Hu Nicole Rodriguez Cavero Sohee Chun Ephraim Gau James F. Steiner Michal Dovčiak |
| author_facet | Henric Krawczynski Yajie Yuan Alexander Y. Chen Kun Hu Nicole Rodriguez Cavero Sohee Chun Ephraim Gau James F. Steiner Michal Dovčiak |
| author_sort | Henric Krawczynski |
| collection | DOAJ |
| description | The Imaging X-ray Polarimetry Explorer observations of the X-ray binary 4U 1630–47 in the high soft state revealed high linear polarization degrees (PDs) rising from 6% at 2 keV to 10% at 8 keV. We discuss in this Letter three different mechanisms that impact the polarization of the observed X-rays: the reflection of gravitationally lensed emission by the accretion disk, reprocessing of the emission in outflowing plasma, and electron and ion anisotropies in the accretion disk atmosphere. We conducted detailed ray-tracing studies to evaluate the impact of the reflection of strongly gravitationally lensed emission on the PDs. Although the reflected emission can produce high PDs in the high-energy tail of the thermal emission component, we do not find models that describe the PDs and are consistent with independent estimates of the source distance. We discuss the energetics of another proposed mechanism: the emission or scattering of the X-rays in mildly relativistically moving plasma outflows. We argue that these models are disfavored as they require large mechanical luminosities on the order of, or even exceeding, the Eddington luminosity. We investigated the impact of electron and ion anisotropies but find that their impact on the observed PDs are likely negligible. We conclude with a discussion of all three effects and avenues for future research. |
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| issn | 2041-8205 |
| language | English |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal Letters |
| spelling | doaj-art-0b8f2047b19b4f069df1e95d87dedf3e2025-08-20T02:38:51ZengIOP PublishingThe Astrophysical Journal Letters2041-82052024-01-019771L1010.3847/2041-8213/ad855cEvaluation of Several Explanations of the Strong X-Ray Polarization of the Black Hole X-Ray Binary 4U 1630-47Henric Krawczynski0https://orcid.org/0000-0002-1084-6507Yajie Yuan1https://orcid.org/0000-0002-0108-4774Alexander Y. Chen2https://orcid.org/0000-0002-4738-1168Kun Hu3https://orcid.org/0000-0002-9705-7948Nicole Rodriguez Cavero4https://orcid.org/0000-0001-5256-0278Sohee Chun5https://orcid.org/0009-0002-2488-5272Ephraim Gau6https://orcid.org/0000-0002-5250-2710James F. Steiner7https://orcid.org/0000-0002-5872-6061Michal Dovčiak8https://orcid.org/0000-0003-0079-1239Physics Department, McDonnell Center for the Space Sciences, and Center for Quantum Leaps, Washington University in St. Louis , St. Louis, MO 63130, USA ; krawcz@wustl.eduPhysics Department and McDonnell Center for the Space Sciences, Washington University in St. Louis , St. Louis, MO 63130, USA ; yajiey@wustl.edu, cyuran@wustl.eduPhysics Department and McDonnell Center for the Space Sciences, Washington University in St. Louis , St. Louis, MO 63130, USA ; yajiey@wustl.edu, cyuran@wustl.eduPhysics Department, McDonnell Center for the Space Sciences, and Center for Quantum Leaps, Washington University in St. Louis , St. Louis, MO 63130, USA ; krawcz@wustl.eduPhysics Department, McDonnell Center for the Space Sciences, and Center for Quantum Leaps, Washington University in St. Louis , St. Louis, MO 63130, USA ; krawcz@wustl.eduPhysics Department, McDonnell Center for the Space Sciences, and Center for Quantum Leaps, Washington University in St. Louis , St. Louis, MO 63130, USA ; krawcz@wustl.eduPhysics Department, McDonnell Center for the Space Sciences, and Center for Quantum Leaps, Washington University in St. Louis , St. Louis, MO 63130, USA ; krawcz@wustl.eduHarvard-Smithsonian Center for Astrophysics , 60 Garden Street, Cambridge, MA 02138, USAAstronomical Institute of the Czech Academy of Sciences , Boční II 1401/1, 14100 Praha 4, Czech RepublicThe Imaging X-ray Polarimetry Explorer observations of the X-ray binary 4U 1630–47 in the high soft state revealed high linear polarization degrees (PDs) rising from 6% at 2 keV to 10% at 8 keV. We discuss in this Letter three different mechanisms that impact the polarization of the observed X-rays: the reflection of gravitationally lensed emission by the accretion disk, reprocessing of the emission in outflowing plasma, and electron and ion anisotropies in the accretion disk atmosphere. We conducted detailed ray-tracing studies to evaluate the impact of the reflection of strongly gravitationally lensed emission on the PDs. Although the reflected emission can produce high PDs in the high-energy tail of the thermal emission component, we do not find models that describe the PDs and are consistent with independent estimates of the source distance. We discuss the energetics of another proposed mechanism: the emission or scattering of the X-rays in mildly relativistically moving plasma outflows. We argue that these models are disfavored as they require large mechanical luminosities on the order of, or even exceeding, the Eddington luminosity. We investigated the impact of electron and ion anisotropies but find that their impact on the observed PDs are likely negligible. We conclude with a discussion of all three effects and avenues for future research.https://doi.org/10.3847/2041-8213/ad855cGeneral relativityStellar mass black holesBlack holesHigh energy astrophysicsBlack hole physicsPlasma astrophysics |
| spellingShingle | Henric Krawczynski Yajie Yuan Alexander Y. Chen Kun Hu Nicole Rodriguez Cavero Sohee Chun Ephraim Gau James F. Steiner Michal Dovčiak Evaluation of Several Explanations of the Strong X-Ray Polarization of the Black Hole X-Ray Binary 4U 1630-47 The Astrophysical Journal Letters General relativity Stellar mass black holes Black holes High energy astrophysics Black hole physics Plasma astrophysics |
| title | Evaluation of Several Explanations of the Strong X-Ray Polarization of the Black Hole X-Ray Binary 4U 1630-47 |
| title_full | Evaluation of Several Explanations of the Strong X-Ray Polarization of the Black Hole X-Ray Binary 4U 1630-47 |
| title_fullStr | Evaluation of Several Explanations of the Strong X-Ray Polarization of the Black Hole X-Ray Binary 4U 1630-47 |
| title_full_unstemmed | Evaluation of Several Explanations of the Strong X-Ray Polarization of the Black Hole X-Ray Binary 4U 1630-47 |
| title_short | Evaluation of Several Explanations of the Strong X-Ray Polarization of the Black Hole X-Ray Binary 4U 1630-47 |
| title_sort | evaluation of several explanations of the strong x ray polarization of the black hole x ray binary 4u 1630 47 |
| topic | General relativity Stellar mass black holes Black holes High energy astrophysics Black hole physics Plasma astrophysics |
| url | https://doi.org/10.3847/2041-8213/ad855c |
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