Discovery of a New Spectral Transition in Swift J0243.6+6124 in the Sub-Eddington Regime
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arXiv
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| Format: | Preprint |
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2026
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| _version_ | 1866918318800109568 |
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| author | Chen, Bo-Yan Zhang, Shu Shui, Qing-Cang Wang, Peng-Ju Ji, Long Kong, Ling-Da Zhang, Shuang-Nan Feng, Hua Chen, Yu-Peng Ge, Ming-Yu Peng, Jing-Qiang Li, Wen-zhong |
| author_facet | Chen, Bo-Yan Zhang, Shu Shui, Qing-Cang Wang, Peng-Ju Ji, Long Kong, Ling-Da Zhang, Shuang-Nan Feng, Hua Chen, Yu-Peng Ge, Ming-Yu Peng, Jing-Qiang Li, Wen-zhong |
| contents | We conduct a detailed spectral analysis of the Galactic ultraluminous X-ray pulsar Swift J0243.6+6124 in its sub-Eddington regime, using Insight-HXMT and NICER observations during multiple outbursts including the 2018 giant outburst. We discover a new transition at $L_{\rm t} \approx 4.5 \times 10^{37}\ {\rm erg\ s^{-1}}$, accompanied by systematic evolution of spectral parameters, in particular a significant turnover in the blackbody normalization. This transition luminosity in the sub-Eddington regime represents the fifth transition identified so far in Swift J0243.6+6124, further highlighting the complexity of its accretion-powered emission. We interpret the transition in terms of a multipolar magnetic-field configuration, where weak ($\sim 2.8 \times 10^{12}\ {\rm G}$) and strong ($\sim 1.6 \times 10^{13}\ {\rm G}$) magnetic poles dominate the emission at different accretion rates. On the magnetospheric scale, this configuration is equivalent to an effective dipole field of $\sim 6.6 \times 10^{12}\ {\rm G}$, while allowing the local surface field to exceed $10^{13}\ {\rm G}$. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2602_01702 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Discovery of a New Spectral Transition in Swift J0243.6+6124 in the Sub-Eddington Regime Chen, Bo-Yan Zhang, Shu Shui, Qing-Cang Wang, Peng-Ju Ji, Long Kong, Ling-Da Zhang, Shuang-Nan Feng, Hua Chen, Yu-Peng Ge, Ming-Yu Peng, Jing-Qiang Li, Wen-zhong High Energy Astrophysical Phenomena We conduct a detailed spectral analysis of the Galactic ultraluminous X-ray pulsar Swift J0243.6+6124 in its sub-Eddington regime, using Insight-HXMT and NICER observations during multiple outbursts including the 2018 giant outburst. We discover a new transition at $L_{\rm t} \approx 4.5 \times 10^{37}\ {\rm erg\ s^{-1}}$, accompanied by systematic evolution of spectral parameters, in particular a significant turnover in the blackbody normalization. This transition luminosity in the sub-Eddington regime represents the fifth transition identified so far in Swift J0243.6+6124, further highlighting the complexity of its accretion-powered emission. We interpret the transition in terms of a multipolar magnetic-field configuration, where weak ($\sim 2.8 \times 10^{12}\ {\rm G}$) and strong ($\sim 1.6 \times 10^{13}\ {\rm G}$) magnetic poles dominate the emission at different accretion rates. On the magnetospheric scale, this configuration is equivalent to an effective dipole field of $\sim 6.6 \times 10^{12}\ {\rm G}$, while allowing the local surface field to exceed $10^{13}\ {\rm G}$. |
| title | Discovery of a New Spectral Transition in Swift J0243.6+6124 in the Sub-Eddington Regime |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2602.01702 |