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Please use this identifier to cite or link to this item: http://hdl.handle.net/2289/8620
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dc.contributor.authorHu, Chin-Ping-
dc.contributor.authorOta, Naoyuki-
dc.contributor.authorTakahashi, T-
dc.contributor.authorTakeda, Tomoshi-
dc.contributor.authorEnoto, Teruaki-
dc.contributor.authorTamagawa, Toru-
dc.contributor.authorPaul, Biswajit-
dc.contributor.authorWatanabe, Sota-
dc.contributor.authorIwakiri, Wataru-
dc.contributor.authorMihara, Tatehiro-
dc.contributor.authorAoyama, Amira-
dc.contributor.authorIwata, Satoko-
dc.contributor.authorYamasaki, Kaede-
dc.contributor.authorKita, Takayuki-
dc.contributor.authorTsuchiya, Soma-
dc.contributor.authorIchibakase, Mayu-
dc.contributor.authorNinjaSat collaboration-
dc.date.accessioned2026-02-11T04:30:56Z-
dc.date.available2026-02-11T04:30:56Z-
dc.date.issued2025-12-17-
dc.identifier.citationThe Astrophysical Journal, 2025, Vol.995 (2), AR No. 202en_US
dc.identifier.issn1538-4357-
dc.identifier.urihttp://hdl.handle.net/2289/8620-
dc.descriptionOpen Access. Also available at arXiv.org (one of the alternative locations)en_US
dc.description.abstractWe 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 nonstationary superorbital modulation with periods ranging from approximately 40 to 65 days. Its peak luminosity of 1.3 × 1039 erg s−1 makes it a local analog of ultraluminous X-ray pulsars powered by supercritical accretion. We find that the spinup rate during the high state remains consistent with the long-term average, with no significant correlation between the spinup 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 a variable covering fraction, due to geometric obscuration, or by free precession of the neutron star. This represents the first complete measurement of the spinup rate and spectral evolution across a single superorbital cycle in SMC X-1, highlighting the scientific capability of CubeSat-based observatories.en_US
dc.language.isoenen_US
dc.publisherThe Astrophysical Journalen_US
dc.relation.urihttps://doi.org/10.48550/arXiv.2511.05016en_US
dc.relation.urihttp://doi.org/10.3847/1538-4357/ae1ca6en_US
dc.rights2025 The Astrophysical Journalen_US
dc.titleUnveiling the Nature of Superorbital Modulation of SMC X-1 Using NinjaSaten_US
dc.typeArticleen_US
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