Measurement of Vector Magnetic Field in a Flare kernel with a Spectropolarimetric Observation in He I 10830 A

Abstract

A flare kernel associated with a C4 class flare was observed in a spectral window including the He I triplet 10830 A and Si I 10827 A with a spectropolarimeter on the Domeless Solar Telescope at Hida Observatory on August 9th, 2015. Observed Stokes profiles of the He I triplet in the flare kernel in its post-maximum phase are well reproduced through inversions considering the Zeeman and the Paschen-Back effects with a three slab model of the flare kernel, in which two slabs having up and downward velocities produce emissions and one slab produces an absorption. The magnetic field strength inferred from the emission components of the He I line is 1400 G, which is significantly stronger than 690 G that is observed at the same location in the same line 6.5 hours before the flare. In addition, photospheric magnetic field vector derived from the Si I10827 A is similar to that of the flare kernel. To explain this results, we suggest that the emission in the He I triplet during the flare is produced in the deep layer, around which bombardment of non-thermal electrons leads to the formation of a coronal temperature plasma. Assuming a hydrogen column density at the location where the He I emissions are formed, and a power-law index of non-thermal electron energy distribution, we derived the low-energy cutoff of the non-thermal electron as 20 - 30 keV, which is consistent with that inferred from hard X-ray data obtained by RHESSI.

arXiv comment15 pages, 8 figures, 1 table, accepted for publication in PASJ (Hida topical issue)

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Cited by in corpus (5)

• Comparison of Enhanced Absorption in He I 10830 Å in Observations and Modeling During the Early Phase of a Solar Flare
• Chromospheric velocities in an M3.2 flare using He I 1083.0 nm and Ca II 854.2 nm
• Infrequent Occurrence of Significant Linear Polarization in H$\alpha$ Solar Flares
• On the center-to-limb variations of the He I 10830 Å triplet
• Infrared spectropolarimetry of a C-class solar flare footpoint plasma -- I. Spectral features and forward modelling