Material mixing in pulsar wind nebulae of massive runaway stars

ABSTRACT In this study we quantitatively examine the manner pulsar wind, supernova ejecta, and defunct stellar wind materials distribute and melt together into plerions. We performed 2.5D magnetohydrodynamical simulations of the entire evolution of their stellar surroundings and different scenarios are explored, whether the star dies as a red supergiant and Wolf–Rayet supernova progenitors, and whether it moved with velocity 20 or $40\, \rm km\, \rm s^{-1}$ through the interstellar medium. Within the post-explosion, early $10\, \rm kyr$, the H-burning-products rich red supergiant wind only mixes by $\le 20~{{\rm per\ cent}}$, due to its dense circumstellar medium filling the progenitor’s bow shock trail, still unaffected by the supernova blast wave. Wolf–Rayet materials, enhanced in C, N, O elements, distribute circularly for the $35\, \rm M_\odot$ star moving at $20\, \rm km\, \rm s^{-1}$ and oblongly at higher velocities, mixing efficiently up to 80 per cent. Supernova ejecta, filled with Mg, Si, Ca, Ti, and Fe, remain spherical for longer times at $20\, \rm km\, \rm s^{-1}$ but form complex patterns at higher progenitor speeds due to earlier interaction with the bow shock, in which they mix more efficiently. The pulsar wind mixing is more efficient for Wolf–Rayet (25 per cent) than red supergiant progenitors (20 per cent). This work reveals that the past evolution of massive stars and their circumstellar environments critically shapes the internal distribution of chemical elements on plerionic supernova remnants, and, therefore, governs the origin of the various emission mechanisms at work therein. This is essential for interpreting multifrequency observations of atomic and molecular spectral lines, such as in optical, infrared, and soft X-rays.