2026ApJ...998L..15L

PSR J2021+4026 is a remarkable γ-ray pulsar exhibiting repeated transitions between high γ-ray flux (HGF) and low γ-ray flux (LGF) states. With 17 yr Fermi Large Area Telescope monitoring, we reveal persistent secular evolution and enhanced spin-down rate variability within individual emission states-beneath the quasiperiodic state transitions. After removing discrete jumps, the jump-corrected flux δF_γ shows a three-phase evolution: rise ($+2.0{2}_{-0.15}^{+0.17} \% \,{{\rm{yr}}}^{-1}$), decline ($-3.7{2}_{-0.47}^{+0.34} \% \,{{\rm{yr}}}^{-1}$), and rapid rise ($+14.{9}_{-4.4}^{+6.4} \% \,{{\rm{yr}}}^{-1}$), with all rates quoted relative to the long-term mean flux 〈F_γ〉 = 7.8 × 10^–10 erg cm^–2 s^–1. Moreover, the flux of the LGF state is gradually approaching the stable HGF level at a rate of +0.72% ± 0.11% yr^–1. These results demonstrate that secular flux evolution in PSR J2021+4026 operates largely independently of discrete state transitions, yet jointly with them drives the system toward a stable high-flux equilibrium.