# Formation and eruption of sigmoidal structure from a weak field region of NOAA 11942

## TL;DR

This study investigates the formation and eruption of a sigmoidal magnetic structure in NOAA 11942, revealing how small-scale flux cancelation and reconnection lead to a slow CME and weak flare, emphasizing the role of gradual energy release.

## Contribution

It provides detailed observational evidence of sigmoid formation and eruption driven by flux cancelation and tether-cutting reconnection in a weak field region, highlighting slow eruption dynamics.

## Key findings

- Sigmoid formed from small-scale flux cancelation and shearing motions.
- Eruption was associated with a slow CME and weak C1.0 flare.
- Energy release occurred over an extended period, indicating gradual reconnection.

## Abstract

Using observations from Solar Dynamics Observatory, we studied an interesting example of a sigmoid formation and eruption from small-scale flux canceling regions of active region (AR) 11942. Analysis of HMI and AIA observations infer that initially the AR is compact and bipolar in nature, evolved to sheared configuration consisting of inverse J-shaped loops hosting a filament channel over a couple of days. By tracking the photospheric magnetic features, shearing and converging motions are observed to play a prime role in the development of S-shaped loops and further flux cancellation leads to tether-cutting reconnection of J-loops. This phase is co-temporal with the filament rise motion followed by sigmoid eruption at 21:32 UT on January 6. The flux rope rises in phases of slow (v$_{avg}$ = 26 km~s$^{-1}$) and fast (a$_{avg}$= 55 ms$^{-2}$) rise motion categorizing the CME as slow with an associated weak C1.0 class X-ray flare. The flare ribbon separation velocity peaks at around peak time of the flare at which maximum reconnection rate (2.14 Vcm$^{-1}$) occurs. Further, the EUV light-curves of 131, 171\AA~have delayed peaks of 130 minutes compared to 94\AA~and is explained by differential emission measure. Our analysis suggests that the energy release is proceeded in a much long time duration, manifesting the onset of filament rise and eventual eruption driven by converging and canceling flux in the photosphere. Unlike strong eruption events, the observed slow CME and weak flare are indications of slow runway tether-cutting reconnection where most of the sheared arcade is relaxed during the extended post phase of the eruption.