Evolution of the Inner Accretion Flow in Swift J1727.8$-$1613 across Intermediate States: Insights from Broadband Spectral and Timing Analysis
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2025
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| author | Chand, Swadesh Zdziarski, Andrzej A. Dewangan, Gulab C. Sahu, Pragati |
| author_facet | Chand, Swadesh Zdziarski, Andrzej A. Dewangan, Gulab C. Sahu, Pragati |
| contents | We present a comprehensive broadband spectral and variability study of the newly detected black hole X-ray binary Swift~J1727.8--1613 in the intermediate states during its 2023 outburst, using multi-mission observations from NICER, NuSTAR, AstroSat, and Insight-HXMT. Spectral data up to 78 keV in the hard-intermediate state (HIMS) require models with two Comptonizing regions. In contrast, models with a single Comptonizing region adequately describe the soft-intermediate states (SIMS), implying a significant evolution in the disk-corona geometry between the states. The hard X-ray tail above $100$ keV in the HIMS, detected with both AstroSat/CZTI and Insight-HXMT/HE, indicates that the electron population in the corona is not purely thermal but rather hybrid, with a power-law distribution above the thermal cutoff. While both the reflection modeling and disk continuum fitting favor a truncated disk geometry in the HIMS, the disk in the SIMS moves substantially closer to the innermost stable circular orbit, accompanied by a significant rise in disk temperature. This interpretation is further supported by the increase in the QPO frequency from $\sim1.3$ to $\sim6.6$ Hz. From joint modeling of the disk continuum and reflection component and assuming the distance of 3.4 kpc, we estimate a black hole mass of $10.3^{+5.5}_{-2.5}~M_\odot$, spin of $0.79^{+0.07}_{-0.15}$, and the disk inclination angle of $\sim37\degr$--$53\degr$, which match well with the previously reported spectro-polarimetric measurements. We find a weakly variable or stable disk and a highly variable Comptonized component. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2512_05544 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Evolution of the Inner Accretion Flow in Swift J1727.8$-$1613 across Intermediate States: Insights from Broadband Spectral and Timing Analysis Chand, Swadesh Zdziarski, Andrzej A. Dewangan, Gulab C. Sahu, Pragati High Energy Astrophysical Phenomena We present a comprehensive broadband spectral and variability study of the newly detected black hole X-ray binary Swift~J1727.8--1613 in the intermediate states during its 2023 outburst, using multi-mission observations from NICER, NuSTAR, AstroSat, and Insight-HXMT. Spectral data up to 78 keV in the hard-intermediate state (HIMS) require models with two Comptonizing regions. In contrast, models with a single Comptonizing region adequately describe the soft-intermediate states (SIMS), implying a significant evolution in the disk-corona geometry between the states. The hard X-ray tail above $100$ keV in the HIMS, detected with both AstroSat/CZTI and Insight-HXMT/HE, indicates that the electron population in the corona is not purely thermal but rather hybrid, with a power-law distribution above the thermal cutoff. While both the reflection modeling and disk continuum fitting favor a truncated disk geometry in the HIMS, the disk in the SIMS moves substantially closer to the innermost stable circular orbit, accompanied by a significant rise in disk temperature. This interpretation is further supported by the increase in the QPO frequency from $\sim1.3$ to $\sim6.6$ Hz. From joint modeling of the disk continuum and reflection component and assuming the distance of 3.4 kpc, we estimate a black hole mass of $10.3^{+5.5}_{-2.5}~M_\odot$, spin of $0.79^{+0.07}_{-0.15}$, and the disk inclination angle of $\sim37\degr$--$53\degr$, which match well with the previously reported spectro-polarimetric measurements. We find a weakly variable or stable disk and a highly variable Comptonized component. |
| title | Evolution of the Inner Accretion Flow in Swift J1727.8$-$1613 across Intermediate States: Insights from Broadband Spectral and Timing Analysis |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2512.05544 |