Flare induced penumbra formation in the sunspot of NOAA 10838

TL;DR

This study observes the formation of penumbrae in a sunspot following a flare, suggesting magnetic field relaxation due to reconnection as a key mechanism in penumbra development.

Contribution

It provides observational evidence linking flare-induced magnetic relaxation to penumbra formation in sunspots, highlighting a possible causal relationship.

Findings

Penumbrae formed concurrently with a C-class flare.

Magnetic field relaxation observed during flare events.

Reduction in magnetic twist (α) associated with penumbra formation.

Abstract

We have observed formation of penumbrae on a pore in the active region NOAA10838 using Dunn Solar Telescope at NSO,Sunpot,USA. Simultaneous observations using different instruments (DLSP,UBF,Gband and CaK) provide us with vector magnetic field at photosphere, intensity images and Doppler velocity at different heights from photosphere to chromosphere. Results from our analysis of this particular data-set suggests that penumbrae are formed as a result of relaxation of magnetic field due to a flare happening at the same time. Images in \Halpha\ show the flare (C 2.9 as per GOES) and vector magnetic fields show a re-orientation and reduction in the global $\alpha$ value (a measure of twist). We feel such relaxation of loop structures due to reconnections or flare could be one of the way by which field lines fall back to the photosphere to form penumbrae.