Detection of X-Ray Polarization in the Hard State of IGR J17091-3624: Spectropolarimetric Study with IXPE and NuSTAR Data
The class-transition Galactic X-ray binary IGR J17091–3624 was simultaneously monitored by the Imaging X-ray Polarimetry Explorer (IXPE) and NuSTAR satellites. We present a detailed spectropolarimetric study of the source using data from both satellites covering the period from 2025 March 7 to 10. A...
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2025-01-01
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| author | Dipak Debnath Subham Srimani Hsiang-Kuang Chang |
| author_facet | Dipak Debnath Subham Srimani Hsiang-Kuang Chang |
| author_sort | Dipak Debnath |
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| description | The class-transition Galactic X-ray binary IGR J17091–3624 was simultaneously monitored by the Imaging X-ray Polarimetry Explorer (IXPE) and NuSTAR satellites. We present a detailed spectropolarimetric study of the source using data from both satellites covering the period from 2025 March 7 to 10. A polarimetric analysis in the 2–8 keV band using a model-independent method reveals a significant detection of polarization degree (PD) of (11.3 ± 2.35)% at a polarization angle (PA) of $82\mathop{.}\limits^{^\circ }7\pm 5\mathop{.}\limits^{^\circ }96$ (significant at >4 σ ). The model-dependent polarization analysis using the polconst and polpow models yields consistent values of PD and PA. In both methods, an energy-dependent increasing trend of PD is observed. In the 6–8 keV band, a maximum PD of (29.9 ± 8.46)% (significant at >3 σ ) is detected at a PA of 88 $\mathop{.}\limits^{\unicode{x000b0}}$ 0 ± 8 $\mathop{.}\limits^{\unicode{x000b0}}$ 15 (>3 σ ). The joint spectral analysis using IXPE and NuSTAR data in the 2–70 keV band was performed with four different sets of phenomenological and physical models. Our results indicate a strong dominance of nonthermal photons originating from a “hot” Compton cloud, suggesting that the source was in a hard spectral state. Spectral fitting with the physical kerrbb and TCAF models provides an estimate of the black hole mass ${M}_{{\rm{BH}}}=14.{8}_{-3.4}^{+4.7}\,{M}_{\odot }$ and dimensionless spin parameter a ^* ∼ 0.54. The requirement of a higher hydrogen column density in the spectral fit of the second NuSTAR observation is attributed to the obscuration of nonthermal photons during the dip phase, likely caused by the presence of wind accreted from the companion star. |
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| institution | Kabale University |
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| language | English |
| publishDate | 2025-01-01 |
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| spelling | doaj-art-2142ecf2e42c4edcab4e3d13a9813e9e2025-08-20T04:00:48ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01989216510.3847/1538-4357/adf1e6Detection of X-Ray Polarization in the Hard State of IGR J17091-3624: Spectropolarimetric Study with IXPE and NuSTAR DataDipak Debnath0https://orcid.org/0000-0003-1856-5504Subham Srimani1https://orcid.org/0009-0004-5915-3789Hsiang-Kuang Chang2https://orcid.org/0000-0002-5617-3117Institute of Astronomy, National Tsing Hua University , Hsinchu 300044, Taiwan ; dipakcsp@gmail.com; Institute of Astronomy Space and Earth Science , P 177, CIT Road, Scheme 7m, Kolkata 700054, IndiaInstitute of Astronomy, National Tsing Hua University , Hsinchu 300044, Taiwan ; dipakcsp@gmail.comInstitute of Astronomy, National Tsing Hua University , Hsinchu 300044, Taiwan ; dipakcsp@gmail.com; Department of Physics, National Tsing Hua University , Hsinchu 300044, TaiwanThe class-transition Galactic X-ray binary IGR J17091–3624 was simultaneously monitored by the Imaging X-ray Polarimetry Explorer (IXPE) and NuSTAR satellites. We present a detailed spectropolarimetric study of the source using data from both satellites covering the period from 2025 March 7 to 10. A polarimetric analysis in the 2–8 keV band using a model-independent method reveals a significant detection of polarization degree (PD) of (11.3 ± 2.35)% at a polarization angle (PA) of $82\mathop{.}\limits^{^\circ }7\pm 5\mathop{.}\limits^{^\circ }96$ (significant at >4 σ ). The model-dependent polarization analysis using the polconst and polpow models yields consistent values of PD and PA. In both methods, an energy-dependent increasing trend of PD is observed. In the 6–8 keV band, a maximum PD of (29.9 ± 8.46)% (significant at >3 σ ) is detected at a PA of 88 $\mathop{.}\limits^{\unicode{x000b0}}$ 0 ± 8 $\mathop{.}\limits^{\unicode{x000b0}}$ 15 (>3 σ ). The joint spectral analysis using IXPE and NuSTAR data in the 2–70 keV band was performed with four different sets of phenomenological and physical models. Our results indicate a strong dominance of nonthermal photons originating from a “hot” Compton cloud, suggesting that the source was in a hard spectral state. Spectral fitting with the physical kerrbb and TCAF models provides an estimate of the black hole mass ${M}_{{\rm{BH}}}=14.{8}_{-3.4}^{+4.7}\,{M}_{\odot }$ and dimensionless spin parameter a ^* ∼ 0.54. The requirement of a higher hydrogen column density in the spectral fit of the second NuSTAR observation is attributed to the obscuration of nonthermal photons during the dip phase, likely caused by the presence of wind accreted from the companion star.https://doi.org/10.3847/1538-4357/adf1e6X-ray transient sourcesX-ray binary starsPolarimetryBlack holesBlack hole physicsAccretion |
| spellingShingle | Dipak Debnath Subham Srimani Hsiang-Kuang Chang Detection of X-Ray Polarization in the Hard State of IGR J17091-3624: Spectropolarimetric Study with IXPE and NuSTAR Data The Astrophysical Journal X-ray transient sources X-ray binary stars Polarimetry Black holes Black hole physics Accretion |
| title | Detection of X-Ray Polarization in the Hard State of IGR J17091-3624: Spectropolarimetric Study with IXPE and NuSTAR Data |
| title_full | Detection of X-Ray Polarization in the Hard State of IGR J17091-3624: Spectropolarimetric Study with IXPE and NuSTAR Data |
| title_fullStr | Detection of X-Ray Polarization in the Hard State of IGR J17091-3624: Spectropolarimetric Study with IXPE and NuSTAR Data |
| title_full_unstemmed | Detection of X-Ray Polarization in the Hard State of IGR J17091-3624: Spectropolarimetric Study with IXPE and NuSTAR Data |
| title_short | Detection of X-Ray Polarization in the Hard State of IGR J17091-3624: Spectropolarimetric Study with IXPE and NuSTAR Data |
| title_sort | detection of x ray polarization in the hard state of igr j17091 3624 spectropolarimetric study with ixpe and nustar data |
| topic | X-ray transient sources X-ray binary stars Polarimetry Black holes Black hole physics Accretion |
| url | https://doi.org/10.3847/1538-4357/adf1e6 |
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