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

• Published in: The Astrophysical journal Vol. 832; no. 2; pp. 174 - 192
• Main 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, Tomas, Gehrels, Neil
• Format: Journal Article
• Language: English
• Published: Goddard Space Flight Center The American Astronomical Society 01.12.2016; IOP Publishing
• Subjects: Astronomical models; ASTROPHYSICS; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Bandpass; BINARY STARS; Blackbody; BREMSSTRAHLUNG; COMPUTERIZED SIMULATION; DWARF STARS; Emissions; Extrasolar planets; FLARING; HARD X RADIATION; High temperature plasmas; HOT PLASMA; KEV RANGE; Optical properties; Photosphere; Planetary atmospheres; Radio waves; Red dwarf stars; SATELLITES; stars: coronae; stars: flare; stars: individual (DG CVn); STELLAR FLARES; TELESCOPES; TRANSIENTS; VISIBLE RADIATION; WAVELENGTHS; White light; X-RAY SPECTRA; X-rays; Stars: Coronae €“ Stars: Flare €“ Stars: Individual (dg Cvn)
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/0004-637X/832/2/174

ABSTRACT 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 TX 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 >1020 cm2, 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 ∼ 104 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 × 1035 and 9 × 1035 erg, and optical flare energies at EV of 2.8 × 1034 and 5.2 × 1034 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.