Pre-eruption Processes: Heating, Particle Acceleration, and the Formation of a Hot Channel before the 2012 October 20 M9.0 Limb Flare

Abstract

We report a detailed study of the pre-eruption activities that led to the occurrence of an M9.0 flare/CME event on 2012 October 20 in NOAA AR 11598. This includes the study of the preceding confined C2.4 flare that occurred on the same AR ∼25 minutes earlier. We observed that the M9.0 flare occurred as a consequence of two distinct triggering events well separated in time. The first triggering episode occurred as early as ∼20 minutes before the onset of the M9.0 flare, evidenced by the destabilization and rise of a pre-existing filament to a new position of equilibrium at a higher coronal altitude during the decay phase of the C2.4 flare. This brought the system to a magnetic configuration where the establishment of the second triggering event was favorable. The second triggering episode occurred ∼17 minutes later, during the early phase of the M9.0 flare, evidenced by the further rise of the filament and successful ejection. The second trigger is followed by a flare precursor phase, characterized by non-thermal emission and the sequential formation of a hot channel as shown by the SDO/AIA DEM (differential emission measure) maps, the RHESSI X-ray images and spectra. These observations are suggestive of magnetic reconnection and particle acceleration that can explain the precursor phase and can be directly related to the formation of the hot channel. We discuss on the triggering mechanisms, their implications during the early and precursor phases and highlight the importance of early activities and preceding small confined flares to understand the initiation of large eruptive flares.

A Hot Cusp-shaped Confined Solar Flare

“…3(b,c)), indicative of accelerated electrons prior to the flare onset (in agreement with e.g. Li et al 2018a;Hernandez-Perez et al 2019). This suggests that reconfiguration of the magnetic field due to pre-flare reconnection caused the strong magnetic reconnection and triggered SOL2014-01-13T21:51M1.3 at L2.…”

“…Flare precursors are enhanced pre-flare soft X-ray (SXR) emission indicative of small-scale energy release that may play a role in the triggering of the main flare (e.g. van Hoven & Hurford 1984;Veronig et al 2002;Joshi et al 2016;Hernandez-Perez et al 2019). Three precursor episodes (GOES-class B7.4, B7.0 and B7.9) were registered by GOES and RHESSI during the early phase of the M1.3 flare under study (see enhanced 6-12 and 12-25 keV precursor emission highlighted by the yellow and blue areas in the top panel of Fig.…”

Preflare Processes, Flux Rope Activation, Large-scale Eruption, and Associated X-class Flare from the Active Region NOAA 11875

“…Pre-flare activities prior to a flare are considered to be important in order to understand the physical conditions that lead to flares and associated eruptions (Fárník et al 1996;Fárník & Savy 1998;Fárník et al 2003;Chifor et al 2006Chifor et al , 2007Joshi et al 2011Joshi et al , 2013. Contemporary studies, dealing with the analysis of X-ray images and spectra during the mild pre-flare X-ray emission (Joshi et al 2013;Hernandez-Perez et al 2019), suggest pre-flare phase to be associated with the events of small-scale magnetic reconnection that can potentially destabilize the flux ropes as described in different models of solar eruptions (i.e., tether-cutting and breakout reconnection models). Our analysis suggests that the location of the pre-flare event 'P1' was associated with consistent EUV brightening along with thermal X-ray sources (Figure 4) suggesting continuous small-scale reconnection events in a localized region that resulted into the eruption of the hot channel (i.e.…”

HXR emission from an activated flux rope and subsequent evolution of an eruptive long duration solar flare

“…Subsequently, the hot channel undergoes significant intensity enhancement and starts to appear in X-ray images up to 25 keV energies. Coronal pre-flare activity starts with the initiation of intense emission from the MFR and surrounding regions (an observational fact that has traditionally been observed in SXR as enhanced emission; see e.g., Veronig et al 2002;Chifor et al 2007;Hernandez-Perez et al 2019;Joshi et al 2011Joshi et al , 2013.…”