Phase-drifting with emitting plasma temperature in the quasi-periodic pulsations of an X-class solar flare.

Recent multi-wavelength observations of solar flares have provided new constraints on the physical origin of quasi-periodic pulsations (QPPs). In an X-class flare, we detect a short-lived approximately 5-min QPP simultaneously in hard X-rays, extreme-ultraviolet (EUV) and soft X-ray emissions, exhibiting a clear phase-drifting behaviour with emitting plasma temperature. Based on phase-resolved timing analysis, it is found that (i) the QPPs in all diagnostics share nearly identical oscillation periods, (ii) a systematic temperature-dependent phase drifting is present, with the phase delay relative to the hard X-ray emission increases systematically from the hottest to cooler EUV channels, and (iii) the QPP persists for only a few cycles during the impulsive phase. These properties imply that periodic magnetic reconnection, possibly triggered by the leakage of 5-min oscillations from the lower atmosphere, modulates the non-thermal electrons responsible for the leading hard X-ray QPPs. Subsequently, plasma heating and cooling processes manifest sequentially across passbands with different temperature responses, resulting in the observed temperature-dependent phase drifting. These results provide novel observational evidence supporting the use of multi-temperature, multi-wavelength phase relationships to constrain the temporal evolution of flare energy release and the origins of QPPs. This article is part of the theme issue 'Transferable mechanisms in the oscillatory processes of solar and stellar flares'.