We conducted four-night multiwavelength observations of an active M-dwarf star EV Lacertae on 2022 October 24–27 with simultaneous coverage of soft X-rays (NICER; 0.2–12 keV, Swift XRT; 0.2–10 keV), near-ultraviolet (Swift UVOT/UVW2; 1600–3500 Å), optical photometry (TESS; 6000–10000 Å), and optical spectroscopy (Nayuta/MALLS; 6350–6800 Å). During the campaign, we detected a flare starting at 12:28 UTC on October 25 with a white-light bolometric energy of 3.4 × 1032 erg. At about 1 h after this flare peak, our Hα spectrum showed a blueshifted excess component at a corresponding velocity of ∼100 km s−1. This may indicate that the prominence erupted with a 1 h delay of the flare peak. Furthermore, the simultaneous 20 s cadence near-ultraviolet (NUV) and white-light curves show gradual and rapid brightening behaviors during the rising phase at this flare. The ratio of flux in NUV to white light at the gradual brightening was ∼0.49, which may suggest that the temperature of the blackbody is low (<9000 K) or the maximum energy flux of a non-thermal electron beam is less than 5 × 1011 erg cm−2 s−1. Our simultaneous observations of the NUV and white-light flare raise the issue of a simple estimation of UV flux from optical continuum data by using a blackbody model.

中文翻译：

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活跃M矮星EV Lacertae及其伴随延迟日珥喷发的恒星耀斑的多波长观测

我们于 2022 年 10 月 24-27 日对一颗活跃的 M 矮星 EV Lacertae 进行了四晚多波长观测，同时覆盖软 X 射线（NICER；0.2-12 keV，Swift XRT；0.2-10 keV）、近紫外（Swift UVOT/UVW2；1600–3500 Å）、光学光度测定（TESS；6000–10000 Å）和光谱学（Nayuta/MALLS；6350–6800 Å）。在活动期间，我们检测到 10 月 25 日 12:28 UTC 开始的耀斑，其白光辐射热能量为 3.4 × 1032 erg。在这个耀斑峰值后约 1 小时，我们的 Hα 光谱显示出蓝移的过量成分，相应的速度为 ∼100 km s−1。这可能表明日珥爆发时耀斑峰值延迟了 1 小时。此外，同步的 20 秒节奏近紫外线 (NUV) 和白光曲线显示出在该耀斑上升阶段逐渐和快速的增亮行为。逐渐增亮时 NUV 与白光的通量比约为 0.49，这可能表明黑体的温度较低（<9000 K）或非热电子束的最大能量通量小于 5 × 1011 erg cm−2 s−1。我们对 NUV 和白光耀斑的同时观测提出了使用黑体模型根据光学连续谱数据简单估计 UV 通量的问题。