Please use this identifier to cite or link to this item:
http://hdl.handle.net/2289/8620| Title: | Unveiling the Nature of Superorbital Modulation of SMC X-1 Using NinjaSat |
| Authors: | Hu, Chin-Ping Ota, Naoyuki Takahashi, T 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 NinjaSat collaboration |
| Issue Date: | 17-Dec-2025 |
| Publisher: | The Astrophysical Journal |
| Citation: | The Astrophysical Journal, 2025, Vol.995 (2), AR No. 202 |
| Abstract: | 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 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. |
| Description: | Open Access. Also available at arXiv.org (one of the alternative locations) |
| URI: | http://hdl.handle.net/2289/8620 |
| ISSN: | 1538-4357 |
| Alternative Location: | https://doi.org/10.48550/arXiv.2511.05016 http://doi.org/10.3847/1538-4357/ae1ca6 |
| Copyright: | 2025 The Astrophysical Journal |
| Appears in Collections: | Research Papers (A&A) |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| Unveiling the Nature of Superorbital Modulation of SMC X-1 Using NinjaSat.pdf Restricted Access | Open Access | 969.62 kB | Adobe PDF | View/Open Request a copy |
Items in RRI Digital Repository are protected by copyright, with all rights reserved, unless otherwise indicated.