CompositeSNRs

CompositeSNRs are a class of supernova remnants that exhibit both a shell-like outer structure and a central pulsar wind nebula (PWN). They represent a middle ground between shell-type remnants, which are dominated by the forward shock, and plerionic or Crab-like remnants, which are powered primarily by a central pulsar without a prominent shell.

The outer shell arises from the forward shock as the supernova blast wave interacts with the surrounding interstellar or circumstellar medium. The inner component, the PWN, is a nebula of synchrotron-emitting electrons and positrons injected by a rapidly spinning neutron star (pulsar) and terminated by a standing shock where the wind pressure balances the ambient medium. The PWN often appears as a filled-center, non-thermal emission region inside the fainter, filamentary shell. The pulsar’s proper motion can lead to an offset between the PWN and the geometric center of the shell.

Observationally, composite SNRs show radio and X-ray emission from both components. The shell can display thermal emission with emission lines and filamentary structure, while the PWN emits non-thermal radiation that may include torus- and jet-like features in X-rays. Gamma-ray emission can originate from the PWN via inverse-Compton scattering, and in some cases from the shell as well.

Evolution and morphology are shaped by the interaction between the PWN and the supernova ejecta, as well as the reverse shock propagating back into the nebula. Over time, the PWN can be compressed, distorted, or displaced, leading to a wide variety of appearances.

CompositeSNRs are valuable for studying particle acceleration, pulsar energetics, and the interplay between young neutron stars and their supernova environments. They are cataloged alongside other SNR classes and are identified through coordinated radio, X-ray, and gamma-ray observations.