LEIA Discovery of the Longest-lasting and Most Energetic Stellar X-Ray Flare Ever Detected

• Published in: The Astrophysical journal Vol. 980; no. 2; pp. 268 - 282
• Main Authors: Mao, Xuan, Liu, He-Yang, Wang, Song, Ling, Zhixing, Yuan, Weimin, Cheng, Huaqing, Pan, Haiwu, Li, Dongyue, Favata, Fabio, Ji, Tuo, Zhang, Jujia, Zhao, Xinlin, Wang, Jing, Liu, Mingjun, Liu, Yuan, Cai, Zhiming, Castro-Tirado, Alberto J., Dai, Yanfeng, Deng, Licai, Ding, Xu, Ji, Kaifan, Jin, Chichuan, Lei, Yajuan, Li, Huali, Lin, Jun, Liu, Huaqiu, Liu, Shuai, Sun, Hui, Sun, Shengli, Sun, Xiaojin, Shi, Jianrong, Wang, Jianguo, Wang, Jingxiu, Wang, Wenxin, Wei, Jianyan, Xin, Liping, Xiong, Dingrong, Zhang, Chen, Zhang, Wenda, Zhang, Yonghe, Zhang, Xiaofeng, Zhao, Donghua, Zhou, Guiping
• Format: Journal Article
• Language: English
• Published: The American Astronomical Society 20.02.2025; IOP Publishing
• Subjects: Stellar activity; Stellar flares; X-ray transient sources
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ada698

The Lobster Eye Imager for Astronomy (LEIA) detected a new X-ray transient on 2022 November 7, identified as a superflare event occurring on a nearby K-type giant star HD 251108. The flux increase was also detected in follow-up observations at X-ray, UV, and optical wavelengths. The flare lasted for about 40 days in soft X-ray observations, reaching a peak luminosity of ∼1.1 × 10 34 erg s −1 in 0.5–4.0 keV, which is roughly 60 times the quiescent luminosity. Optical brightening was observed for only one night. The X-ray light curve is well described by a double fast rise and exponential decay model, attributed to the cooling process of a loop arcade structure formed subsequent to the initial large loop with a half-length of ∼1.9 × 10 12 cm. Time-resolved X-ray spectra were fitted by a four-temperature apec model (with three components being the quiescent background), showing significant evolution of plasma temperature and emission measure over time. The estimated energy released in the LEIA band is ∼3 × 10 39 erg, suggesting that this is likely the most energetic X-ray stellar flare with the longest duration detected to date.