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Active regions often show S-shaped structures in the corona called sigmoids.These are highly sheared and twisted loops formed along the polarity inversionline. They are considered to be one of the best pre-eruption signatures forCMEs. Here, we investigate the thermodynamic evolution of an on-disk sigmoidobserved during December 24-28, 2015. For this purpose, we have employedEmission Measure (EM) and filter-ratio techniques on the observations recordedby the Atmospheric Imaging Assembly (AIA) onboard the Solar DynamicsObservatory (SDO) and X-ray Telescope (XRT) onboard Hinode. The EM analysisshowed multi-thermal plasma along the sigmoid and provided a peak temperatureof 10-12.5 MK for all observed flares. The sigmoidal structure showed emissionfrom Fe XVIII (93.93 {\AA}) and Fe XXI 128.75 {\AA}) lines in the AIA 94 and131 {\AA} channels, respectively. Our results show that the hot plasma is oftenconfined to very hot strands. The temperature obtained from the EM analysis wasfound to be in good agreement with that obtained using the XRT, AIA, and GOESfilter-ratio methods. These results provide important constraints for thethermodynamic modeling of sigmoidal structures in the core of active regions.Moreover, this study also benchmarks different techniques available fortemperature estimation in solar coronal structures.

Thermodynamic evolution of a sigmoidal active region with associated flares