THE MOUSE THAT ROARED: A SUPERFLARE FROM THE dMe FLARE STAR EV LAC DETECTED BY SWIFT AND KONUS-WIND

Journal Article · Mon Sep 20 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/721/1/785· OSTI ID:21464817

Osten, Rachel A ^[1]; Godet, Olivier ^[2]; Drake, Stephen; Tueller, Jack; Cummings, Jay; Krimm, Hans ^[3]; Pye, John ^[4]; Pal'shin, Valentin; Golenetskii, Sergei ^[5]; Reale, Fabio ^[6]; Oates, Samantha R; Page, Mat J ^[7]; Melandri, Andrea ^[8]

---

1. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
2. Universite de Toulouse, UPS, CESR, 9 Avenue du Colonel Roche, 31028 Toulouse Cedex 9 (France)
3. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
4. Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom)
5. Ioffe Physico-Technical Institute, Laboratory for Experimental Astrophysics, 26 Polytekhnicheskaya, St. Petersburg 194021 (Russian Federation)
6. Dip. Scienze Fis. and Astron., Sez. Astron., Universita di Palermo, P.za Parlamento 1, 90134 Palermo (Italy)
7. Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT (United Kingdom)
8. Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead CH41 1LD (United Kingdom)

We report on a large stellar flare from the nearby dMe flare star EV Lac observed by the Swift and Konus-Wind satellites and the Liverpool Telescope. It is the first large stellar flare from a dMe flare star to result in a Swift trigger based on its hard X-ray intensity. Its peak f{sub X} from 0.3 to 100 keV of 5.3 x 10{sup -8} erg cm{sup -2} s{sup -1} is nearly 7000 times larger than the star's quiescent coronal flux, and the change in magnitude in the white filter is {>=}4.7. This flare also caused a transient increase in EV Lac's bolometric luminosity (L{sub bol}) during the early stages of the flare, with a peak estimated L{sub X}/L{sub bol} {approx} 3.1. We apply flare loop hydrodynamic modeling to the plasma parameter temporal changes to derive a loop semi-length of l/R{sub *} = 0.37 {+-} 0.07. The soft X-ray spectrum of the flare reveals evidence of iron K{alpha} emission at 6.4 keV. We model the K{alpha} emission as fluorescence from the hot flare source irradiating the photospheric iron, and derive loop heights of h/R{sub *} = 0.1, consistent within factors of a few with the heights inferred from hydrodynamic modeling. The K{alpha} emission feature shows variability on timescales of {approx}200 s which is difficult to interpret using the pure fluorescence hypothesis. We examine K{alpha} emission produced by collisional ionization from accelerated particles, and find parameter values for the spectrum of accelerated particles which can accommodate the increased amount of K{alpha} flux and the lack of observed nonthermal emission in the 20-50 keV spectral region.

• OSTI ID: 21464817
• Journal Information: Astrophysical Journal, Vol. 721, Issue 1; Other Information: DOI: 10.1088/0004-637X/721/1/785; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
BOLOMETERS
FLUORESCENCE
HARD X RADIATION
IONIZATION
IRON
LUMINOSITY
SATELLITES
SIMULATION
SOFT X RADIATION
STARS
STELLAR CORONAE
STELLAR FLARES
TELESCOPES
ATMOSPHERES
ELECTROMAGNETIC RADIATION
ELEMENTS
EMISSION
IONIZING RADIATIONS
LUMINESCENCE
MEASURING INSTRUMENTS
METALS
OPTICAL PROPERTIES
PHOTON EMISSION
PHYSICAL PROPERTIES
RADIATIONS
STELLAR ACTIVITY
STELLAR ATMOSPHERES
TRANSITION ELEMENTS
X RADIATION