Pulsation and quiescent stage labeled by the pulse profile of PSR J2021+4026 (0.7–2 keV) as observed by the XMM-Newton/PN camera. The obtained light curve was folded with a spin frequency of 3.768995206 Hz. Two rotation cycles are shown for clarity. Error bars indicate the 1σ uncertainty. The gray-shaded regions and the blue-shaded regions illustrate the off-pulse phase (i.e., DC level) and the on-pulse phase, respectively. The pulsed spectrum was obtained by subtracting the DC level from the source spectrum extracted from the on-pulse phase interval.