A Transient Coronal Sigmoid and Associated Flare and Coronal Mass Ejection



The formation of a coronal sigmoid is often followed by the explosive energy liberation of dynamic phenomena, such as flare and coronal mass ejection. A recent multi-wavelength study, co-authored by AO Senior Scientist Dr P K Manoharan explains the build-up phase of a sigmoidal flux rope in the corona followed by an intense two-ribbon flare and the eruption of flux rope leading to a fast coronal mass ejection.

A Transient Coronal Sigmoid in Active Region NOAA 11909: Build-up Phase, M-class Eruptive Flare, and Associated Fast Coronal Mass Ejection

Hema Kharayat (1), Bhuwan Joshi (1), Prabir K. Mitra (1), P. K. Manoharan (2 and 3), Christian Monstein (4) ((1) Udaipur Solar Observatory, Physical Research Laboratoy, India, (2) Radio Astronomy Centre, National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, India, (3) Arecibo Observatory, University of Central Florida, Puerto Rico, USA, (4) Istituto Ricerche Solari Locarno (IRSOL), Via Patocchi 57, 6605 Locarno Monti, Switzerland)

In this article, we investigate the formation and disruption of a coronal sigmoid from the active region (AR) NOAA 11909 on 07 December 2013, by analyzing multi-wavelength and multi-instrument observations. Our analysis suggests that the formation of `transient' sigmoid initiated ≈1 hour before its eruption through a coupling between two twisted coronal loop systems. A comparison between coronal and photospheric images suggests that the coronal sigmoid was formed over a simple β-type AR which also possessed dispersed magnetic field structure in the photosphere. The line-of-sight photospheric magnetograms also reveal moving magnetic features, small-scale flux cancellation events near the PIL, and overall flux cancellation during the extended pre-eruption phase which suggest the role of tether-cutting reconnection toward the build-up of the flux rope. The disruption of the sigmoid proceeded with a two-ribbon eruptive M1.2 flare (SOL2013-12-07T07:29). In radio frequencies, we observe type III and type II bursts in meter wavelengths during the impulsive phase of the flare. The successful eruption of the flux rope leads to a fast coronal mass ejection (with a linear speed of ≈1085 km s -1 ) in SOHO/LASCO field-of-view. During the evolution of the flare, we clearly observe typical "sigmoid-to-arcade" transformation. Prior to the onset of the impulsive phase of the flare, flux rope undergoes a slow rise (≈15 km s -1 ) which subsequently transitions into a fast eruption (≈110 km s -1 ). The two-phase evolution of the flux rope shows temporal associations with the soft X-ray precursor and impulsive phase emissions of the M-class flare, respectively, thus pointing toward a feedback relationship between magnetic reconnection and early CME dynamics.
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Keywords: arecibo, observatory, X-ray, NOAA, Coronal, Sigmoid, Manoharan, Eruptive, Flare, ejection, magnetograms, CME, dynamics