The impact of circumstellar wind-blown bubbles on the dynamics of pulsar wind nebulae and supernova remnants

Abstract: The core-collapse supernova explosion of most massive stars is followed by the development of a supernova remnant (SNR) and pulsar wind nebula (PWN) system whose evolution is in part dictated by its surrounding environment. The latter is frequently assumed to be the typical interstellar medium (ISM). However, massive stars emit powerful winds during their lifetime and carve extended circumstellar cavities known as wind-blown bubbles (WBBs). We investigated the impact of WBBs on the dynamics, energetics, and thermal X-ray emission of a SNR-PWN system. We performed numerical simulations of a 1D hydrodynamical analogue of the system, for different stellar progenitors and pulsar parameters, in a WBB or ISM environment. The system initially expands to large sizes in the low-density interior of a WBB, until the SNR fills the entire bubble. The PWN grows to $\gtrsim10~\mathrm{pc}$ ($30~\mathrm{pc}$) after $\sim5~\mathrm{kyr}$ ($\sim25~\mathrm{kyr}$) for a $M=8~\mathrm{M}<em>\odot$ ($M=20~\mathrm{M}</em>\odot$) progenitor, $5-6$ times larger than in an ISM environment. The impact of the SNR on the massive outer shell of the WBB generates a strong reflected shock that efficiently returns energy to the inner parts of the system. At late times, after a strong compression of the PWN by an order of magnitude in size, back-and-forth shock crossings of the cavity maintain the SNR at very high temperatures and drive a vigorous reverberation of the PWN, with changes in radius by up to $3-4$. In this stage, the PWN is on average $2-4$ times larger than in an ISM environment and contains up to an order of magnitude more energy. Thermal radiation from the system occurs in few very localised emission bursts, as low-velocity shocks are transmitted across the bubble shell when it is hit by blast waves. WBBs offer a possible explanation for the large sizes of many PWNe and the non-detection of their parent SNRs.