2025-12-19 京都大学
credit：ひっぐすたん
＜関連情報＞
- https://www.kyoto-u.ac.jp/ja/research-news/2025-12-19
- https://www.kyoto-u.ac.jp/sites/default/files/2025-12/web_2512_Enoto-82d9e173e2be427be673bc1ca7900ba1.pdf
- https://iopscience.iop.org/article/10.3847/1538-4357/ae1699
MAXI-NICER 連携で観測された悪魔の星アルゴルでの恒星フレア食 Eclipsing Stellar Flare on the Demon Star Algol Binary System Observed during the MAXI–NICER Follow-up Campaign in 2018
Kazuya Nakayama, Wataru Buz Iwakiri, Teruaki Enoto, Shun Inoue, Yuta Notsu, Keith Gendreau, Zaven Arzoumanian, Kenji Hamaguchi, and Tatehiro Mihara
The Astrophysical Journal Published: 2025 December 18
DOI:10.3847/1538-4357/ae1699
Abstract
Algol is a well-known eclipsing binary hosting an active and variable star that exhibits frequent stellar flares. Here, we report our preplanned and coordinated rapid X-ray follow-up observations of an eclipsing flare on Algol. The Monitor of All-sky X-ray Image detected a flare on Algol at 05:52 UT on 2018 July 4. Subsequently, we carried out a prompt X-ray monitoring with the Neutron star Interior Composition ExploreR starting at 19:45 UT on the same day, and the observation ended at 06:02 UT on 2018 July 6. During the decaying phase of the flare, we successfully detected a 5.8 hr long eclipse, corresponding to the secondary eclipse in which Algol A blocks the line of sight to Algol B. During the eclipse, the 2–10 keV X-ray flux is decreased to the 20% level from 1.9 × 10−10 to 4.5 × 10−11 erg cm−2 s−1. We found a configuration of the flare size and location to explain the X-ray observations; e.g., the flare occurred at the latitude 45°S of the Algol B surface with a flare height of 1.9 × 1011 cm, corresponding to 0.8 times the stellar radius of Algol B, giving 80% obscuration of the flare loop by Algol A. The apparent absorption increase before the eclipse might originate from coronal mass ejection in the line of sight ejected during the flare.
