Evolution of an eruptive flare loop system

Abstract

Context. Flares, eruptive prominences and coronal mass ejections are phenomena where magnetic reconnection plays an important role. However, the location and the rate of the reconnection, as well as the mechanisms of particle interaction with ambient and chromospheric plasma are still unclear. Aims. In order to contribute to the comprehension of the above mentioned processes we studied the evolution of the eruptive flare loop system in an active region where a flare, a prominence eruption and a CME occurred on August 24, 2002. Methods. We measured the rate of expansion of the flare loop arcade using TRACE 195 Å images and determined the rising velocity and the evolution of the low and high energy hard X-ray sources using RHESSI data. We also fitted HXR spectra and considered the radio emission at 17 and 34 GHZ. Results. We observed that the top of the eruptive flare loop system initially rises with a linear behavior and then, after 120 mn from the start of the event registered by GOES at 1-8 Å, it slows down. We also observed that the heating source (low energy X-ray) rises faster than the top of the loops at 195 Å and that the high energy X-ray emission (30-40 keV) changes in time, changing from footpoint emission at the very onset of the flare to being coincident during the flare peak with the whole flare loop arcade. Conclusions. The evolution of the loop system and of the X-ray sources allowed us to interpret this event in the framework of the Lin & Forbes model (2000), where the absolute rate of reconnection decreases when the current sheet is located at an altitude where the Alfvén speed decreases with height. We estimated that the lower limit for the altitude of the current sheet is 6 × 10 4 km. Moreover, we interpreted the unusual variation of the high energy HXR emission as a manifestation of the non thermal coronal thick-target process which appears during the flare in a manner consistent with the inferred increase in coronal column density.

Radio observations of the fine structure inside a post-CME current sheet

“…The corresponding velocity inferred from the drift rate is comparable to the group-based displacement velocity of the zero-drift stripes in groups IV and V (see Fig. 6(d) and Table 2), and it lies in the range of velocity obtained from studies of the other events (Khan et al 2006(Khan et al , 2007Romano et al 2009;Yan et al 2013). We note that the upward motion of the source in stripe 9 cannot come from an anti-sunward moving plasma blob, because such a blob could not penetrate the newly reconnected field lines carried downward by the reconnection outflow.…”

The Relationship Between Solar Radio and Hard X-ray Emission

“…By far the favorite loop event for radio studies during the RHESSI period is SOL2002-08-24T01:12 (X3.1) on the west limb (Karlický 2004;Li & Gan 2005;Melnikov 2006;Tzatzakis et al 2008;Romano et al 2009;Reznikova et al 2009;, which also produced a fast (1900 km s −1 ) CME and an energetic particle event at the Earth. Figure 5.1 shows images in HXRs, microwaves and the EUV 195Å band (Fe XII and Fe XXIV) during the early part of the impulsive phase, for which RHESSI data are available.…”

Transition Region Emission From Solar Flares During the Impulsive Phase

“…Gamma ray emission detected by SONG began at 00:58 UT, near the time of the O VI peak, and continued for 9 minutes (Kuznetsov et al 2006). Romano et al (2009) studied the evolution of this flare. They found that the prominence became unstable at 00:52 UT, the same time that the RHESSI hard X-rays began to brighten.…”