CXOU J202117.4+364723 , the SIMBAD biblio

We describe recent Chandra ACIS observations of the Vela-like pulsar PSR J2021+3651 and its pulsar wind nebula (PWN). This ``Dragonfly Nebula'' displays an axisymmetric morphology, with bright inner jets, a double-ridged inner nebula, and a ∼30" polar jet. The PWN is embedded in faint diffuse emission: a bow shock-like structure with standoff of ∼1' brackets the pulsar to the east and emission trails off westward for 3'-4'. Thermal (kT_∞=0.16±0.02 keV) and power-law emission are detected from the pulsar. The nebular X-rays show spectral steepening from Γ=1.5 in the equatorial torus to Γ=1.9 in the outer nebula, suggesting synchrotron burnoff. A fit to the Dragonfly structure suggests a large (86°±1°) inclination with a double equatorial torus. Vela is currently the only other PWN showing such double structure. The ∼12 kpc distance implied by the pulsar dispersion measure is not supported by the X-ray data; spectral, scale, and efficiency arguments suggest a more modest 3-4 kpc.