High-velocity Blue-shifted Fe xxv Heα Line during a Superflare of the RS Canum Venaticorum–type Star IM Peg

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書誌事項

公開日
2024-06-26
資源種別
journal article
権利情報
  • http://creativecommons.org/licenses/by/4.0/
  • https://iopscience.iop.org/info/page/text-and-data-mining
DOI
  • 10.3847/2041-8213/ad5667
公開者
American Astronomical Society

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<jats:title>Abstract</jats:title> <jats:p>The Monitor of All-sky X-ray Image (MAXI) detected a superflare, releasing 5 × 10<jats:sup>37</jats:sup> erg in 2−10 keV, of the RS CVn-type star IM Peg at 10:41 UT on 2023 July 23 with its Gas Slit Camera (2−30 keV). We conducted X-ray follow-up observations of the superflare with the Neutron Star Interior Composition Explorer (NICER; 0.2−12 keV) starting at 16:52 UT on July 23 until 06:00 UT on August 2. NICER X-ray spectra clearly showed emission lines of the Fe <jats:sc>xxv</jats:sc> He<jats:italic>α</jats:italic> and Fe <jats:sc>xxvi</jats:sc> Ly<jats:italic>α</jats:italic> for ∼1.5 days since the MAXI detection. The Fe XXV He<jats:italic>α</jats:italic> line was blueshifted with its maximum Doppler velocity reaching −2200 ± 600 km s<jats:sup>−1</jats:sup>, suggesting an upward-moving plasma during the flare, such as a coronal mass ejection (CME) and/or chromospheric evaporation. This is the first case that the Fe <jats:sc>xxv</jats:sc> He<jats:italic>α</jats:italic> line is blueshifted during a stellar flare, and its velocity overwhelmingly exceeds the escape velocity of the star (−230 km s<jats:sup>−1</jats:sup>). One hour before the most pronounced blueshift detection, a signature of the reheating of the flare plasma was observed. We discuss the origin of the blueshift, a CME, or high-velocity chromospheric evaporation.</jats:p>

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