Aditya-L1 and SDO Observations of a Confined X-Class Flare with an EUV Late Phase: Thermal and Nonthermal Emission, Magnetic Topology, and Flux Rope Confinement
We study a long-duration, confined X2.0-class solar flare exhibiting three distinct episodes of HXR emission, along with an accompanying EUV late phase. A key highlight of this work is the novel observations from the high-resolution solar X-ray spectrometers SoLEXS and HEL1OS onboard Aditya-L1, providing insights into the evolution of thermal and non-thermal emissions. Simultaneous EUV observations from AIA/SDO in hot channels, combined with multi-band X-ray light curves, reveal a two-stage confined eruption of a large MFR, separated by $\sim$10~minutes. The first stage corresponds to an M4.6 flare, while the overall event reaches X2.0 on the GOES scale. During the first phase, magnetic reconnection beneath the large EUV hot channel causes plasma heating to $\sim$19~MK, with a non-thermal spectral index of $\sim$4.3. In the second phase, characterized by external reconnection and confinement of the MFR hot channel, the temperature increases to $\sim$22~MK, accompanied by further hardening of the spectral index to $\sim$3.9. Despite pronounced non-thermal signatures and enhanced particle acceleration, the MFR fails to erupt through the overlying coronal loops because of the strong strapping force exerted by the large overlying coronal loops. Importantly, the stalled eruption, together with reconnection in the higher overlying loops, results in enhanced heating within a closed magnetic configuration, with temperatures peaking at up to $\sim$15~MK during the late phase. The paper also provides the first observations of detectable non-thermal X-ray emission during the early EUV late phase, albeit briefly, providing direct evidence for reconnection-induced heating, likely occurring in the higher overlying coronal loops.