2021/03/01 by Ryo Sasaki, Yohko Tsuboi, Wataru Iwakiri +16
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Flare #Flare star #Neutron star #Sky #Solar flare #Star (game theory) #Stellar, planetary, and galactic studies #astro-ph.HE #astro-ph.SR
paper · pdf · doi:10.3847/1538-4357/abde38
17 pages, 9 figures, 4 tables, Published for publication in The Astrophysical Journal (23-Mar-2021)
openalex publication_date 2021/03/01 · openalex created_date 2021/03/29 · arxiv created 2021/03/31 · arxiv updated 2021/04/01 · openalex updated_date 2026/08/05
Abstract We report that the RS CVn–type star GT Mus (HR 4492, HD 101379+HD 101380) was the most active star in the X-ray sky in the last decade in terms of the scale of recurrent energetic flares. We detected 11 flares from GT Mus in 8 yr of observations with the Monitor of All-sky X-ray Image (MAXI) from 2009 August to 2017 August. The detected flare peak luminosities were 1–4 × 10 33 erg s −1 in the 2.0–20.0 keV band for its distance of 109.6 pc. Our timing analysis showed long durations ( τ r + τ d ) of 2–6 days with long decay times ( τ d ) of 1–4 days. The released energies during the decay phases of the flares in the 0.1–100 keV band were in the range of 1–11 × 10 38 erg, which are at the upper end of the observed stellar flare. The released energies during the whole duration were in the range of 2–13 × 10 38 erg in the same band. We carried out X-ray follow-up observations for one of the 11 flares with the Neutron star Interior Composition Explorer (NICER) on 2017 July 18 and found that the flare cooled quasi-statically. On the basis of a quasi-static cooling model, the flare loop length is derived to be 4 × 10 12 cm (or 60 R ☉ ). The electron density is derived to be 1 × 10 10 cm −3 , which is consistent with the typical value of solar and stellar flares (10 10–13 cm −3 ). The ratio of the cooling timescales between radiative ( τ rad ) and conductive ( τ cond ) cooling is estimated to be τ rad ∼ 0.1 τ cond from the temperature; thus, radiative cooling was dominant in this flare.