A VERY BRIGHT, VERY HOT, AND VERY LONG FLARING EVENT FROM THE M DWARF BINARY SYSTEM DG CVn

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Authors	OSTEN Rachel A. KOWALSKI Adam DRAKE Stephen A. KRIMM Hans PAGE Kim GAZEAS Kosmas KENNEA Jamie OATES Samantha PAGE Mathew DE MIGUEL Enrique NOVÁK Rudolf APELTAUER Tomáš GEHRELS Neil
Year of publication	2016
Type	Article in Periodical
Magazine / Source	Astrophysical Journal
MU Faculty or unit	Faculty of Science
Citation
Web	http://iopscience.iop.org/article/10.3847/0004-637X/832/2/174/meta;jsessionid=AB7A964C666CBD80C6B55F9810D105F7.c2.iopscience.cld.iop.org
Doi	http://dx.doi.org/10.3847/0004-637X/832/2/174
Field	Astronomy and astrophysics
Keywords	stars: coronae; stars: flare; stars: individual (DG CVn)
Description	On 2014 April 23, the Swift satellite responded to a hard X-ray transient detected by its Burst Alert Telescope, which turned out to be a stellar flare from a nearby, young M dwarf binary DG CVn. We utilize observations at X-ray, UV, optical, and radio wavelengths to infer the properties of two large flares. The X-ray spectrum of the primary outburst can be described over the 0.3-100 keV bandpass by either a single very high-temperature plasma or a nonthermal thick-target bremsstrahlung model, and we rule out the nonthermal model based on energetic grounds. The temperatures were the highest seen spectroscopically in a stellar flare, at T-X of 290 MK. The first event was followed by a comparably energetic event almost a day later. We constrain the photospheric area involved in each of the two flares to be >10(20) cm(2), and find evidence from flux ratios in the second event of contributions to the white light flare emission in addition to the usual hot, T similar to 10(4) K blackbody emission seen in the impulsive phase of flares. The radiated energy in X-rays and white light reveal these events to be the two most energetic X-ray flares observed from an M dwarf, with X-ray radiated energies in the 0.3-10 keV bandpass of 4 x 10(35) and 9 x 10(35) erg, and optical flare energies at E-V of 2.8 x 10(34) and 5.2 x 10(34) erg, respectively. The results presented here should be integrated into updated modeling of the astrophysical impact of large stellar flares on close-in exoplanetary atmospheres.