X-ray transients and flares from active stellar systems
Many X-ray flares detected to date from active cool stars were initially discovered as fast (≲ 3 hour) transients1,2,3. A survey of the HEAO A-1 Sky Survey Experiment 0.5–20 keV data for fast transients confirms the tendency for a significant fraction of such events to be associated with active stellar systems. Eight months of the mission (which include one full scan of the sky) were searched, yielding 10 transients of which three are identified with flares on cool stars. Of the remaining sources4, all but ones5 are at least consistent in their X-ray properties with a stellar flare origin.
We discuss below the three fast transients which we have identified with active stellar systems. They are EV Lac, a dM4.5e flare star (d = 5 pc)6, HD 8357, an RS CVn type binary (d ∼ 70 pc)7, and EQ Vir (BD-7°3646), a dK5 flare star (d = 16 pc)8.
KeywordsLight Curve Cool Star Flare Star Fast Transient Small Flare
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