Detection of X-ray Polarization in the Hard State of IGR J17091-3624: Spectro-Polarimetric Study with IXPE and NuSTAR Data
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2025
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| _version_ | 1866911053406797824 |
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| author | Debnath, Dipak Srimani, Subham Chang, Hsiang-Kuang |
| author_facet | Debnath, Dipak Srimani, Subham Chang, Hsiang-Kuang |
| contents | The class-transition Galactic X-ray binary IGR~J17091--3624 was simultaneously monitored by the \textit{IXPE} and \textit{NuSTAR} satellites. We present a detailed spectro-polarimetric study of the source using data from both satellites covering the period from March~7--10, 2025. A polarimetric analysis in the $2$--$8$~keV band using a model-independent method reveals a significant detection of polarization degree (PD) of $(11.3\pm2.35)\%$ at a polarization angle (PA) of $82^\circ.7\pm5^\circ.96$ (significant at $>4σ$). The model-dependent polarization analysis using the \texttt{polconst} and \texttt{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 $(29.9\pm8.46)\%$ (significant at $>3σ$) is detected at a PA of $88^\circ.0\pm8^\circ.15$ ($>3σ$). The joint spectral analysis using \textit{IXPE} and \textit{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 non-thermal photons originating from a `hot' Compton cloud, suggesting that the source was in a hard spectral state. Spectral fitting with the physical {\fontfamily{qcr}\selectfont kerrbb} and {\fontfamily{qcr}\selectfont TCAF} models provides an estimate of the black hole mass $M_{\rm BH} = 14.8^{+4.7}_{-3.4}~M_\odot$ and dimensionless spin parameter $a^* \sim 0.54$. The requirement of a higher hydrogen column density in the spectral fit of the second \textit{NuSTAR} observation is attributed to the obscuration of non-thermal photons during the dip phase, likely caused by the presence of wind accreted from the companion star. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2504_16402 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Detection of X-ray Polarization in the Hard State of IGR J17091-3624: Spectro-Polarimetric Study with IXPE and NuSTAR Data Debnath, Dipak Srimani, Subham Chang, Hsiang-Kuang High Energy Astrophysical Phenomena The class-transition Galactic X-ray binary IGR~J17091--3624 was simultaneously monitored by the \textit{IXPE} and \textit{NuSTAR} satellites. We present a detailed spectro-polarimetric study of the source using data from both satellites covering the period from March~7--10, 2025. A polarimetric analysis in the $2$--$8$~keV band using a model-independent method reveals a significant detection of polarization degree (PD) of $(11.3\pm2.35)\%$ at a polarization angle (PA) of $82^\circ.7\pm5^\circ.96$ (significant at $>4σ$). The model-dependent polarization analysis using the \texttt{polconst} and \texttt{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 $(29.9\pm8.46)\%$ (significant at $>3σ$) is detected at a PA of $88^\circ.0\pm8^\circ.15$ ($>3σ$). The joint spectral analysis using \textit{IXPE} and \textit{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 non-thermal photons originating from a `hot' Compton cloud, suggesting that the source was in a hard spectral state. Spectral fitting with the physical {\fontfamily{qcr}\selectfont kerrbb} and {\fontfamily{qcr}\selectfont TCAF} models provides an estimate of the black hole mass $M_{\rm BH} = 14.8^{+4.7}_{-3.4}~M_\odot$ and dimensionless spin parameter $a^* \sim 0.54$. The requirement of a higher hydrogen column density in the spectral fit of the second \textit{NuSTAR} observation is attributed to the obscuration of non-thermal photons during the dip phase, likely caused by the presence of wind accreted from the companion star. |
| title | Detection of X-ray Polarization in the Hard State of IGR J17091-3624: Spectro-Polarimetric Study with IXPE and NuSTAR Data |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2504.16402 |