Unveiling the Nature of Superorbital Modulation of SMC X-1 using NinjaSat
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| Main Authors: | , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866909892122509312 |
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| author | Hu, Chin-Ping Ota, Naoyuki Takahashi, Takuya Takeda, Tomoshi Enoto, Teruaki Tamagawa, Toru Paul, Biswajit Watanabe, Sota Iwakiri, Wataru Mihara, Tatehiro Aoyama, Amira Iwata, Satoko Yamasaki, Kaede Kita, Takayuki Tsuchiya, Soma Ichibakase, Mayu |
| author_facet | Hu, Chin-Ping Ota, Naoyuki Takahashi, Takuya Takeda, Tomoshi Enoto, Teruaki Tamagawa, Toru Paul, Biswajit Watanabe, Sota Iwakiri, Wataru Mihara, Tatehiro Aoyama, Amira Iwata, Satoko Yamasaki, Kaede Kita, Takayuki Tsuchiya, Soma Ichibakase, Mayu |
| contents | We report a long-term, high-cadence timing and spectral observation of the X-ray pulsar SMC X-1 using NinjaSat, a 6U CubeSat in low-Earth orbit, covering nearly a full superorbital cycle. SMC X-1 is a high-mass X-ray binary exhibiting a 0.7 s X-ray pulsar and a non-stationary superorbital modulation with periods ranging from approximately 40 to 65 days. Its peak luminosity of $1.3\times10^{39}$~\lumcgs\ makes it a local analogue of ultraluminous X-ray pulsars powered by supercritical accretion. We find that the spin-up rate during the high state remains consistent with the long-term average, with no significant correlation between spin-up rate and flux. This result indicates that the modulation is primarily geometric rather than accretion-driven. The hardness ratio and spectral shape are stable throughout the entire superorbital cycle, supporting obscuration by optically thick material or energy-independent scattering. In addition, the 2--20 keV pulse profile varies with superorbital phase, which may be explained either by variable covering fraction due to geometric obscuration, or by free precession of the neutron star. This represents the first complete measurement of spin-up rate and spectral evolution across a single superorbital cycle in SMC X-1, highlighting the scientific capability of CubeSat-based observatories. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_05016 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Unveiling the Nature of Superorbital Modulation of SMC X-1 using NinjaSat Hu, Chin-Ping Ota, Naoyuki Takahashi, Takuya Takeda, Tomoshi Enoto, Teruaki Tamagawa, Toru Paul, Biswajit Watanabe, Sota Iwakiri, Wataru Mihara, Tatehiro Aoyama, Amira Iwata, Satoko Yamasaki, Kaede Kita, Takayuki Tsuchiya, Soma Ichibakase, Mayu High Energy Astrophysical Phenomena We report a long-term, high-cadence timing and spectral observation of the X-ray pulsar SMC X-1 using NinjaSat, a 6U CubeSat in low-Earth orbit, covering nearly a full superorbital cycle. SMC X-1 is a high-mass X-ray binary exhibiting a 0.7 s X-ray pulsar and a non-stationary superorbital modulation with periods ranging from approximately 40 to 65 days. Its peak luminosity of $1.3\times10^{39}$~\lumcgs\ makes it a local analogue of ultraluminous X-ray pulsars powered by supercritical accretion. We find that the spin-up rate during the high state remains consistent with the long-term average, with no significant correlation between spin-up rate and flux. This result indicates that the modulation is primarily geometric rather than accretion-driven. The hardness ratio and spectral shape are stable throughout the entire superorbital cycle, supporting obscuration by optically thick material or energy-independent scattering. In addition, the 2--20 keV pulse profile varies with superorbital phase, which may be explained either by variable covering fraction due to geometric obscuration, or by free precession of the neutron star. This represents the first complete measurement of spin-up rate and spectral evolution across a single superorbital cycle in SMC X-1, highlighting the scientific capability of CubeSat-based observatories. |
| title | Unveiling the Nature of Superorbital Modulation of SMC X-1 using NinjaSat |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2511.05016 |