We present a detailed multi-wavelength analysis and interpretation of theevolution of an M7.6 flare on October 24, 2003. The X-ray observations of theflare taken from the RHESSI spacecraft reveal two phases of the flareevolution. The first phase is characterized by the altitude decrease of theX-ray looptop (LT) source for $\sim$11 minutes. Such a long duration of thedescending LT source motion is reported for the first time. The EUV loops,located below the X-ray LT source, also undergo contraction with similar speed($\sim$15 km s$^{-1}$) in this interval. During the second phase the twodistinct hard X-ray footpoints (FP) sources are observed which correlate wellwith UV and H$\alpha$ flare ribbons. The X-ray LT source now exhibits upwardmotion. The RHESSI spectra during the first phase are soft and indicative ofhot thermal emission from flaring loops with temperatures $T>25$ MK at theearly stage. On the other hand, the spectra at high energies ($\varepsilon\gtrsim$25 keV) follow hard power laws during the second phase ($\gamma =2.6-2.8$). We show that the observed motion of the LT and FP sources can beunderstood as a consequence of three-dimensional magnetic reconnection at aseparator in the corona. During the first phase of the flare, the reconnectionreleases an excess of magnetic energy related to the magnetic tensionsgenerated before a flare by the shear flows in the photosphere. The relaxationof the associated magnetic shear in the corona by the reconnection processexplains the descending motion of the LT source. During the second phase, theordinary reconnection process dominates describing the energy release in termsof the standard model of large eruptive flares.
展开▼
