Panel a: (top) rebrightening in 2020 in the 1 − 4 keV and 4 − 10 keV, represented by red and blue curves, respectively. (bottom) Dynamic power density spectrum (PDS) spanning the 1 − 10 keV range. Panel b: (top) the gaps between effective observations were eliminated, due to the extended timescale of the data, to enhance the clarity of the temporal evolution. The figure clearly reveals the presence of mHz QPOs ∼20 mHz, a pattern that aligns with the heartbeat state.