Bow-shock Pulsar Wind Nebulae Passing Through Density Discontinuities

TL;DR

This paper models how bow-shock pulsar wind nebulae, like the Guitar Nebula, form and evolve when pulsars pass through interstellar medium density discontinuities, using hydrodynamic simulations to match observed features.

Contribution

It introduces a new scenario explaining the formation of multiple bubbles in bow-shock nebulae through encounters with density discontinuities, supported by hydrodynamic simulations.

Findings

Reproduced the Guitar Nebula shape with declining low-density regions.

Showed asymmetric bow-shock head formation from inclined density discontinuities.

Simulated bubble formation consistent with observed nebula structures.

Abstract

Bow-shock pulsar wind nebulae are a subset of pulsar wind nebulae that form when the pulsar has high velocity due to the natal kick during the supernova explosion. The interaction between the relativistic wind from the fast-moving pulsar and the interstellar medium produces a bow-shock and a trail, which are detectable in H$_{\alpha}$ emission. Among such bow-shock pulsar wind nebulae, the Guitar Nebula stands out for its peculiar morphology, which consists of a prominent bow-shock head and a series of bubbles further behind. We present a scenario in which multiple bubbles can be produced when the pulsar encounters a series of density discontinuities in the ISM. We tested the scenario using 2-D and 3-D hydrodynamic simulations. The shape of the guitar nebula can be reproduced if the pulsar traversed a region of declining low density. We also show that if a pulsar encounters an inclined density discontinuity, it produces an asymmetric bow-shock head, consistent with observations of the bow-shock of the millisecond pulsar J2124-3358.