Deciphering the Nature of the Pulsar Wind Nebula CTB 87 with XMM-Newton

TL;DR

This study uses XMM-Newton observations to analyze the morphology and evolution of the pulsar wind nebula CTB 87, finding no thermal emission from the supernova remnant and modeling its structure with relativistic hydrodynamical simulations.

Contribution

It provides the first X-ray spectral index map of CTB 87 and demonstrates that its morphology can be explained by 2D axisymmetric relativistic hydrodynamical simulations.

Findings

No thermal X-ray emission detected from the SNR.

Spectral properties indicate a ~20 kyr-old relic PWN.

Morphology consistent with expansion into a stellar wind bubble.

Abstract

CTB 87 (G74.9+1.2) is an evolved supernova remnant (SNR) which hosts a peculiar pulsar wind nebula (PWN). The X-ray peak is offset from that observed in radio and lies towards the edge of the radio nebula. The putative pulsar, CXOU~J201609.2+371110, was first resolved with \textit{Chandra} and is surrounded by a compact and a more extended X-ray nebula. Here we use a deep {\textit{XMM-Newton}} observation to examine the morphology and evolutionary stage of the PWN and to search for thermal emission expected from a supernova shell or reverse shock interaction with supernova ejecta. We do not find evidence of thermal X-ray emission from the SNR and place an upper limit on the electron density of 0.05~cm$^{-3}$ for a plasma temperature $kT\sim 0.8$ keV. The morphology and spectral properties are consistent with a $\sim$20~kyr-old relic PWN expanding into a stellar wind-blown bubble. We also present the first X-ray spectral index map from the PWN and show that we can reproduce its morphology by means of 2D axisymmetric relativistic hydrodynamical simulations.