[Paper Review] The population point of view on the evolution of TeV pulsar wind nebulae

S. Klepser, Y. A. Gallant+2 more|Repository KITopen (Karlsruhe Institute of Technology)|Jan 1, 2017

Astrophysics and Cosmic Phenomena3 references3 citations

TL;DR

This study analyzes the population of TeV pulsar wind nebulae (PWNe) using data from the H.E.S.S. Galactic Plane Survey and literature sources, finding a power-law correlation between TeV luminosity and pulsar spin-down power ($L_{1-10\,\text{TeV}} \sim \dot{E}^{0.58 \pm 0.21}$). The results indicate that PWNe expand and dim over time, with flux limits suggesting detection becomes impossible below $\sim 10^{36}\,\text{erg\,s}^{-1}$, and that pulsar-PWN offsets likely result from asymmetric supernova shock crushing rather than proper motion alone.

ABSTRACT

To investigate the nature and evolution of TeV pulsar wind nebulae, we examine the firmly identified PWNe in the H.E.S.S. Galactic Plane Survey, along with the few other known detections from the literature, as well as the upper limits extracted from the H.E.S.S survey. These data exhibit a correlation of TeV surface brightness with pulsar spin-down power. It appears to be caused by both an increase of TeV extension and a decrease of TeV luminosity with decreasing spin-down power. We also find that the offsets of pulsars with ages around 10 kyr with respect to the wind nebula centres are frequently larger than can be plausibly explained by pulsar proper motion and could be due to an asymmetric environment. These and other results will be presented and put to context with a basic modelling of TeV pulsar wind nebula evolution.

Motivation & Objective

• To understand the evolutionary trends of TeV pulsar wind nebulae (PWNe) across a population of sources.
• To determine whether observed correlations between PWN properties and pulsar spin-down power are consistent with theoretical models.
• To assess the role of environmental asymmetries in causing pulsar-PWN offsets beyond what is explainable by proper motion.
• To quantify the detectability threshold of PWNe based on flux upper limits from undetected systems.
• To evaluate the consistency of observed PWN properties with a simple time-dependent emission model.

Proposed method

• Analyzed 14 firmly identified PWNe and 10 candidate sources from the H.E.S.S. Galactic Plane Survey (HGPS), supplemented by literature detections.
• Compiled flux upper limits for 22 pulsars with $\dot{E} > 10^{35}\,\text{erg\,s}^{-1}$ and expected angular extensions < $0.6^\circ$.
• Applied a one-zone, time-dependent emission model to simulate PWN evolution, varying 12 free parameters including electron injection and cooling.
• Compared observed trends in TeV luminosity, extension, and offsets to model predictions across pulsar ages up to tens of kiloyears.
• Used spectral energy distribution (SED) modeling to decompose emission contributions from different injection epochs in middle-aged PWNe.
• Evaluated the influence of environmental factors such as inhomogeneous media and reverse shock fronts on PWN morphology and offset.

Experimental results

Research questions

• RQ1 Is there a measurable correlation between TeV luminosity and pulsar spin-down power across the PWN population?
• RQ2 To what extent do PWN expansion and luminosity decay explain the non-detection of older or less powerful PWNe?
• RQ3 Can pulsar proper motion alone account for observed offsets between pulsars and their nebulae?
• RQ4 How do flux upper limits for undetected PWNe constrain the evolution of TeV emission over time?
• RQ5 What role does asymmetric supernova shock interaction play in distorting and displacing PWNe?

Key findings

• A power-law correlation between TeV luminosity and pulsar spin-down power was observed, with $L_{1-10\,\text{TeV}} \sim \dot{E}^{0.58 \pm 0.21}$, consistent with a theoretical model predicting a slope near 0.5.
• Flux upper limits indicate that PWNe with pulsar spin-down power below $\sim 10^{36}\,\text{erg\,s}^{-1}$ are undetectable with current instruments, suggesting a luminosity decay with age.
• Pulsar-PWN offsets in systems of ~10 kyr age exceed those expected from proper motion alone, indicating a dominant role for asymmetric reverse shock crushing.
• The observed spread in PWN extension and luminosity is well reproduced by a simple time-dependent model with moderate parameter variation, supporting its basic validity.
• Modeling shows that middle-aged PWNe (e.g., 10 kyr) exhibit complex SEDs dominated by contributions from multiple electron injection epochs, with the 1–10 TeV band peaking in the middle of the nebula's lifetime.
• The study highlights that environmental factors such as local interstellar medium density and background radiation likely influence PWN brightness, as seen in anomalies like faint 3C 58 and bright N 157B.