A nominally confined X6.4 flare associated with an extremely faint coronal mass ejection

¹ State Key Laboratory of Solar Activity and Space Weather, National Astronomical Observatories, Chinese Academy of Sciences, A20 Chaoyang District, Beijing 100101, China
² University of Chinese Academy of Sciences, Beijing 100049, China

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 1 March 2026
Accepted: 6 May 2026

Abstract

Context. The observational distinction between eruptive and confined solar flares is often based on whether a coronal mass ejection (CME) can be identified in coronagraph data. However, CME detectability depends strongly on viewing geometry, coronal background, and instrumental sensitivity, so some physically eruptive events may appear confined during routine inspection.

Aims. We investigate the physical nature of a confined-like X6.4 flare that occurred on 2024 February 22 in NOAA Active Region 13590 and examine why its associated CME is exceptionally faint in coronagraph observations.

Methods. We analyzed the event using multiwavelength observations from SDO/AIA, SDO/HMI, CHASE Hα, GOES-16, SOHO/LASCO, and complementary STEREO-A data. We furthermore employed differential emission measure (DEM) diagnostics and nonlinear force-free field (NLFFF) extrapolations to characterize the thermal and magnetic structure of the eruption.

Results. The event occurred in a magnetically complex active region containing at least three eruptive branches rooted along distinct polarity inversion lines (PILs1–3). Flare brightening first appeared near PIL2, indicating that this branch was involved in triggering the X6.4 flare. However, only the branch associated with PIL1 escaped successfully and produced an extremely faint CME, whereas the branches associated with PIL2 and PIL3 failed and fell back to the solar surface. The successful eruption propagated eastward and was accompanied by pronounced coronal dimming and a fast extreme ultraviolet front, while the failed branches remained confined beneath stronger overlying closed fields. Filamentary structures, hot-channel signatures, DEM results, and NLFFF extrapolations together suggest the presence of three flux-rope-like configurations along the three PILs. The faint CME first becomes identifiable in LASCO only after careful discrimination from repeated backside eruptions using complementary viewpoints.

Conclusions. This event shows that a major flare may appear nominally confined during routine coronagraph inspection while still being physically associated with a CME. In this case, the flare-triggering branch and the CME-producing branch are not the same eruptive component, but belong to a sympathetic sequence in a complex active region. Our results highlight how a flare–CME association can be obscured by both magnetic complexity and CME detectability, and they emphasize the need for multiwavelength and multi-viewpoint diagnostics when assessing whether apparently confined major flares are truly noneruptive.