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Title:
Magnetic Reconnection During the Two-phase Evolution of a Solar Eruptive Flare
Authors:
Joshi, Bhuwan; Veronig, Astrid; Cho, K.-S.; Bong, S.-C.; Somov, B. V.; Moon, Y.-J.; Lee, Jeongwoo; Manoharan, P. K.; Kim, Y.-H.
Affiliation:
AA(Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea ; Udaipur Solar Observatory, Physical Research Laboratory, Udaipur 313 001, India ; ), AB(IGAM/Institute of Physics, University of Graz, Universitätsplatz 5, A-8010 Graz, Austria ), AC(Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea ), AD(Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea ), AE(Astronomical Institute, Moscow State University, Universitetskij Prospekt 13, Moscow 119992, Russia ), AF(School of Space Research, Kyung Hee University, Yongin 446-701, Korea ), AG(Physics Department, New Jersey Institute of Technology, 161 Warren Street, Newark, NJ 07102, USA ), AH(Radio Astronomy Centre, Tata Institute of Fundamental Research, Udhagamandalam (Ooty) 643 001, India), AI(Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea )
Publication:
The Astrophysical Journal, Volume 706, Issue 2, pp. 1438-1450 (2009). (ApJ Homepage)
Publication Date:
12/2009
Origin:
IOP
ApJ Keywords:
Sun: corona, Sun: flares, Sun: X-rays, gamma rays
DOI:
10.1088/0004-637X/706/2/1438
Bibliographic Code:
2009ApJ...706.1438J

Abstract

We present a detailed multi-wavelength analysis and interpretation of the evolution of an M7.6 flare that occurred near the southeast limb on 2003 October 24. Pre-flare images at TRACE 195 Å show that the bright and complex system of coronal loops already existed at the flaring site. The X-ray observations of the flare taken from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft reveal two phases of the flare evolution. The first phase is characterized by the altitude decrease of the X-ray looptop (LT) source for ~11 minutes. Such a long duration of the descending LT source motion is reported for the first time. The EUV loops, located below the X-ray LT source, also undergo contraction with similar speed (~15 km s–1) in this interval. During the second phase the two distinct hard X-ray footpoint (FP) sources are observed which correlate well with UV and Hα flare ribbons. The X-ray LT source now exhibits upward motion as anticipated from the standard flare model. The RHESSI spectra during the first phase are soft and indicative of hot thermal emission from flaring loops with temperatures T > 25 MK at the early stage. On the other hand, the spectra at high energies (ε gsim 25 keV) follow hard power laws during the second phase (γ = 2.6-2.8). We show that the observed motion of the LT and FP sources can be understood as a consequence of three-dimensional magnetic reconnection at a separator in the corona. During the first phase of the flare, the reconnection releases an excess of magnetic energy related to the magnetic tensions generated before a flare by the shear flows in the photosphere. The relaxation of the associated magnetic shear in the corona by the reconnection process explains the descending motion of the LT source. During the second phase, the ordinary reconnection process dominates describing the energy release in terms of the standard model of large eruptive flares with increasing FP separation and upward motion of the LT source.
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