X-ray/H$\alpha$ scaling relationships in stellar flares

Abstract

We report on the results of our simultaneous observations of three large stellar flares with soft X-rays (SXRs) and an H$\alpha$ emission line from two binary systems of RS CVn type. The energies released in the X-ray and H$\alpha$ emissions during the flares were $10^{36}$--$10^{38}$ and $10^{35}$--$10^{37}$ erg, respectively. It renders the set of the observations as the first successful simultaneous X-ray/H$\alpha$ observations of the stellar flares with energies above $10^{35}$ erg; although the coverage of the H$\alpha$ observations of the stellar flares with energies above $10^{35}$ erg; although the coverage of the H$\alpha$ observations was limited, with $\sim$10\% of the $e$-folding time in the decay phase of the flares, that of the SXR ones was complete. Combining the obtained physical parameters and those in literature for solar and stellar flares, we obtained a good proportional relation between the emitted energies of X-ray and H$\alpha$ emissions for a flare energy range of $10^{29}$--$10^{38}$ erg. The ratio of the H$\alpha$-line to bolometric X-ray emissions was $\sim$0.1, where the latter was estimated by converting the observed SXR emission to that in the 0.1--100 keV band according to the best-fitting thin thermal model. We also found that the $e$-folding times of the SXR and H$\alpha$ light curves in the decaying phase of a flare are in agreement for a time range of $1$--$10^4$~s. Even very large stellar flares with energies of six orders of magnitude larger than the most energetic solar flares follow the same scaling relationships with solar and much less energetic stellar flares. This fact suggests that their physical parameters can be estimated on the basis of the known physics of solar and stellar flares.

12 pages, 7 figures

References in corpus (7)

• The XMM-Newton serendipitous survey IX. The fourth XMM-Newton serendipitous source catalogue
• Optical and X-ray observations of stellar flares on an active M dwarf AD Leonis with Seimei Telescope, SCAT, NICER and OISTER
• Large X-ray Flares on Stars Detected with MAXI/GSC: A Universal Correlation between the Duration of a Flare and its X-ray Luminosity
• Simultaneous Kepler/K2 and XMM-Netwon observations of superflares in the Pleiades
• The RS CVn type star GT Mus shows most energetic X-ray flares throughout the 2010s
• The morphology of average solar flare time profiles from observations of the Sun's lower atmosphere
• Investigation of magnetic loop structures in the corona of UX Arietis

Cited by in corpus (4)

• Simultaneous X-ray and optical variability of M dwarfs observed with eROSITA and TESS
• Discovery of a new supergiant fast X-ray transient MAXI J0709-159 associated with the Be star LY CMa
• X-ray and Hα superflare on an RS CVn-type star, UX Arietis: Constraint on the flare location from radial velocity change during the flare
• Einstein Probe Discovery of an X-ray Flare from K-type Star PM J23221-0301