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

Abstract

We present a multi-wavelength analysis of the eruption of a hot coronal channel associated with an X1.0 flare (SOL2013-10-28T02:03) from the active region NOAA 11875 by combining observations from AIA/SDO, HMI/SDO, RHESSI, and HiRAS. EUV images at high coronal temperatures indicated the presence of a hot channel at the core of the active region from the early pre-flare phase evidencing the pre-existence of a quasi-stable magnetic flux rope. The hot channel underwent an activation phase after a localized and prolonged pre-flare event occurring adjacent to one of its footpoints. Subsequently, the flux rope continued to rise slowly for ≈16 min during which soft X-ray flux gradually built-up characterizing a distinct precursor phase. The flux rope transitioned from the state of slow rise to the eruptive motion with the onset of the impulsive phase of the X1.0 flare. The eruptive expansion of the hot channel is accompanied by a series of type III radio bursts in association with impulsive rise of strong hard X-ray non-thermal emissions that included explicit hard X-ray sources of energies up to ≈50 keV from the coronal loops and ≈100 keV from their footpoint locations. Our study contains evidence that pre-flare activity occurring within the spatial extent of a stable flux rope can destabilize it toward eruption. Moreover, sudden transition of the flux rope from the state of slow rise to fast acceleration precisely bifurcated the precursor and the impulsive phases of the flare which points toward a feedback relationship between early CME dynamics and the strength of the large-scale magnetic reconnection.

Observations of a prominence eruption and loop contraction

“…Therefore, the existence of prominence can be considered as an indicator of the magnetic FR in solar corona (Schmieder et al 2013;Filippov et al 2015). The relationship between the FR rise and associated radiative signatures has been a topic of considerable interest (e.g., Alexander et al 2006;Liu et al 2009b;Joshi et al 2013Joshi et al , 2016Mitra & Joshi 2019). In particular, comparisons of the location, timing, and strength of high-energy emissions (e.g., temporal and spatial evolution of HXR sources) with respect to the dynamical evolution of the prominence provide critical clues to help understand the characteristics of the underlying energy release phenomena, such as the expected site of magnetic reconnection, particle acceleration, and heating.…”

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

“…Now, the appearance of 'classical' flare signatures, viz., distinct coronal and footpoint HXR sources along with inner flare ribbons formed at both sides of PIL, provide evidence of large-scale magnetic reconnection, which are attributed to the reconnection-opening of overlying field lines (i.e., progression of reconnection in higher coronal fields of the envelope region) stretched by the erupting MFR. The sudden transition in the kinematic evolution of MFR from the phase of slow to fast rise precisely divides the pre-flare and impulsive phase of the flare, which we attribute to the feedback relationship between the early CME dynamics and the strength of the large-scale magnetic reconnection (Temmer et al 2008;Vršnak 2016;Song et al 2018;Mitra & Joshi 2019).…”

“…The statistical studies carried out with SXR images from Yohkoh, revealed three categories of pre-flare activities in terms of source locations: co-spatial, adjacent, and remote (Fárník & Savy 1998;Kim et al 2008). The co-spatial and adjacent cases occurring within few minutes before the main flare are supposed to have direct relevance for the triggering processes related to the main flare (Liu et al 2009;Joshi et al 2011;Mitra & Joshi 2019). Notably, EUV and X-ray images clearly show that the pre-flare brightenings are spatially distributed along the hot channel (i.e., MFR) and within the core field region.…”

“…It has been observed that many flares are associated with pre-flare and precursor activities, which include small-scale brightness enhancements in the flaring region of about a few to tens of minutes prior to its impulsive phase (Veronig et al 2002;Kundu et al 2004;Joshi et al 2011Joshi et al , 2013Mitra et al 2020). While the precursor phase often shows a direct link to the later eruptive phenomenon, the pre-flare activity is viewed as a single or multiple series of small-scale reconnection events within the active region and may indirectly support the eruption by changing the magnetic and plasma conditions favorably (Fárník et al 1996;Fárník & Savy 1998;Chifor et al 2006;Joshi et al 2011Joshi et al , 2013Mitra & Joshi 2019). Arguably the observations of pre-flare or precursor activity have potential to provide insight on the build-up phase of MFR and the triggering mechanism of the subsequent solar eruption.…”

Successive occurrences of quasi-circular ribbon flares in a fan-spine-like configuration involving hyperbolic flux tube

“…Flux ropes are defined by a set of magnetic field lines that are wrapped around each other in a braided fashion or wrapped around a central axis (braided and twisted flux ropes, respectively, see; Prior & Yeates 2016). Observationally, a flux rope can be identified in different forms: filament (Zirin 1988;Martin 1998), prominence (Tandberg-Hanssen 1995;Parenti 2014), coronal cavity (Forland et al 2013;Gibson 2015), hot channel (Zhang et al 2012;Cheng et al 2013;Mitra & Joshi 2019;Sahu et al 2020), coronal sigmoid (Rust & Kumar 1996;Manoharan et al 1996;Joshi et al 2017a;Mitra et al 2018) etc. The processes involved in the triggering of a flux rope from its stable condition and its successive evolution within the source region are rather complex and debatable (see e.g., Chatterjee & Fan 2013; Kumar et al 2016;Prasad et al 2020).…”