Astronomy and Astrophysics – Astronomy
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009spd....40.1906q&link_type=abstract
American Astronomical Society, SPD meeting #40, #19.06; Bulletin of the American Astronomical Society, Vol. 41, p.847
Astronomy and Astrophysics
Astronomy
Scientific paper
We apply a new method to measure the mean magnetic field in flare loops by analyzing multiple-wavelength observations of a two-ribbon flare. The flare exhibits apparent expansion motion of the ribbons in the lower-atmosphere and rising motion of the top of newly formed flare loops observed in X-rays. These apparent motion patterns are signatures of progressive magnetic reconnection proceeding in a macroscopically organized manner, which may be approximated by a 2D model. Therefore, the reconnection rate is expressed in terms of the reconnection electric field E. As the reconnection flux along the newly formed flare loop is conserved, the relation holds that, when averaged over time, E = VrBr = VtBt, where Vr and Br refer to the ribbon expansion speed and magnetic field swept by the ribbons, and Vt and Bt denote the apparent rising speed of the X-ray source and mean magnetic field at the loop top. By directly measuring Vr, Br, and Vt, we find Bt to be 120 and 60 G, respectively, during two emission peaks 5 min apart in the impulsive phase. An estimate of magnetic field in flare loops is also achieved by analyzing the microwave and hard X-ray spectral observations, yielding B = 250, 120 G at the two emission peaks, respectively. The measured B from the microwave spectrum is an appropriately weighted value of magnetic field from the loop top to the loop leg. Therefore, the two methods to evaluate magnetic field in flaring loops produce fully consistent results, which provides evidence that parameters of reconnection rate derived from ribbon motions are quantitatively valid.
This work is supported by NSF grant and by NSF grant ATM-0748428 and NASA grant NNX08AE44G to Montana State University and NSF grants AST-0607544 and ATM-0707319 and NASA grant NNG06GJ40G to New Jersey Institute of Technology.
Fleishman Gregory D.
Gary Dale E.
Qiu Jiong
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