Thermodynamic evolution of a sigmoidal active region with associated flares

Mulay, S. M. , Tripathi, D. and Mason, H. (2021) Thermodynamic evolution of a sigmoidal active region with associated flares. Monthly Notices of the Royal Astronomical Society, 504(1), pp. 1201-1218. (doi: 10.1093/mnras/stab816)

Abstract

Active regions often show S-shaped structures in the corona called sigmoids. These are highly sheared and twisted loops formed along the polarity inversion line. They are considered to be one of the best pre-eruption signatures for CMEs. Here, we investigate the thermodynamic evolution of an on-disk sigmoid observed during December 24-28, 2015. For this purpose, we have employed Emission Measure (EM) and filter-ratio techniques on the observations recorded by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) and X-ray Telescope (XRT) onboard Hinode. The EM analysis showed multi-thermal plasma along the sigmoid and provided a peak temperature of ∼10-12.5 MK for all observed flares. The sigmoidal structure showed emission from Fe XVIII (93.93 Å) and Fe XXI (128.75 Å) lines in the AIA 94 and 131 Å channels, respectively. Our results show that the hot plasma is often confined to very hot strands. The temperature obtained from the EM analysis was found to be in good agreement with that obtained using the XRT, AIA and GOES filter-ratio methods. These results provide important constraints for the thermodynamic modelling of sigmoidal structures in the core of active regions. Moreover, this study also benchmarks different techniques available for temperature estimation in solar coronal structures.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Mulay, Dr Sargam
• Authors: Mulay, S. M., Tripathi, D., and Mason, H.
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Monthly Notices of the Royal Astronomical Society
• Publisher: Oxford University Press
• ISSN: 0035-8711
• ISSN (Online): 1365-2966
• Published Online: 22 March 2021
• Copyright Holders: Copyright © 2021 The Authors
• First Published: First published in Monthly Notices of the Royal Astronomical Society 504(1):1201–1218
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher