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Mirage Sources and Large TeV Halo-Pulsar Offsets: Exploring the Parameter Space

Yiwei Bao, Ruo-Yu Liu, Gwenael Giacinti, Hai-Ming Zhang, Yang Chen

TL;DR

The paper addresses how ultra-relativistic electrons around pulsars propagate in turbulent interstellar magnetic fields, producing mirage TeV halos that challenge symmetric diffusion models. It advances a GPU-accelerated, first-principles test-particle approach for $100\, \mathrm{TeV}$ electrons, incorporating a divergence-free, multi-scale Kolmogorov turbulent field and radiative losses to generate LHAASO-like gamma-ray maps via IC emission. Key findings show that mirage halos and sizable pulsar offsets arise from anisotropic propagation along local field lines and projection effects, with the magnetic-field strength $B$, coherence length $L_c$, and regular-to-turbulent ratio $B_r/B_t$ controlling source multiplicity, separation, and offsets. The work provides a framework to interpret puzzling LHAASO sources and informs cosmic-ray transport near accelerators, while acknowledging simplifications in turbulence modeling and magnetic-field feedback. Overall, it connects microscopic particle dynamics to macroscopic gamma-ray morphologies through quantitative parameter studies.

Abstract

We investigate the asymmetric propagation of 100 TeV electrons (whose radiation mainly concentrates on 20--30 TeV) in turbulent magnetic fields around pulsars, using GPU-accelerated simulations to explore their trajectories and interactions within pulsar wind nebulae and the interstellar medium. Key results include the identification of ``mirage'' sources indicating significant offsets in high-energy emissions from their originating pulsars, challenging the results of traditional symmetric diffusion models. By varying parameters like source distance, magnetic field strength, and electron injection spectral index, the study delineates their effects on observable phenomena such as the probability that a source has at least one mirage around it, as well as the source separation. Our results offer insights into some puzzling sources observed recently by the Large High Altitude Air Shower Observatory (LHAASO), and shed light on the cosmic-ray transport mechanism in the interstellar medium.

Mirage Sources and Large TeV Halo-Pulsar Offsets: Exploring the Parameter Space

TL;DR

The paper addresses how ultra-relativistic electrons around pulsars propagate in turbulent interstellar magnetic fields, producing mirage TeV halos that challenge symmetric diffusion models. It advances a GPU-accelerated, first-principles test-particle approach for electrons, incorporating a divergence-free, multi-scale Kolmogorov turbulent field and radiative losses to generate LHAASO-like gamma-ray maps via IC emission. Key findings show that mirage halos and sizable pulsar offsets arise from anisotropic propagation along local field lines and projection effects, with the magnetic-field strength , coherence length , and regular-to-turbulent ratio controlling source multiplicity, separation, and offsets. The work provides a framework to interpret puzzling LHAASO sources and informs cosmic-ray transport near accelerators, while acknowledging simplifications in turbulence modeling and magnetic-field feedback. Overall, it connects microscopic particle dynamics to macroscopic gamma-ray morphologies through quantitative parameter studies.

Abstract

We investigate the asymmetric propagation of 100 TeV electrons (whose radiation mainly concentrates on 20--30 TeV) in turbulent magnetic fields around pulsars, using GPU-accelerated simulations to explore their trajectories and interactions within pulsar wind nebulae and the interstellar medium. Key results include the identification of ``mirage'' sources indicating significant offsets in high-energy emissions from their originating pulsars, challenging the results of traditional symmetric diffusion models. By varying parameters like source distance, magnetic field strength, and electron injection spectral index, the study delineates their effects on observable phenomena such as the probability that a source has at least one mirage around it, as well as the source separation. Our results offer insights into some puzzling sources observed recently by the Large High Altitude Air Shower Observatory (LHAASO), and shed light on the cosmic-ray transport mechanism in the interstellar medium.
Paper Structure (12 sections, 6 equations, 3 figures)

This paper contains 12 sections, 6 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Method Description
  3. Generating Turbulent Magnetic Fields
  4. Field Generation Method
  5. Multi-Scale Turbulence Implementation
  6. Simulating Particle Propagations
  7. Simulation data analysis
  8. Methods
  9. Source numbers
  10. Source separation and flux ratio
  11. Offsets
  12. Summary and Discussion

Figures (3)

  • Figure 1: Variation of the source numbers $\xi$ with different plasma parameters: (a) electron injection index $\alpha$, (b) total strength of the magnetic field, (c) coherence length of the turbulent field and (d) regular-to-turbulent ratio. The results demonstrate how $\xi$ depends on different parameters and provide insights into the characteristic scale of turbulence structures in the plasma.
  • Figure 2: Scatter plot of the flux ratio $\chi$ and separation distance for different $L_{\rm c}$ (top panel), magnetic field strength $B^2$ (middle panel) and the strength ratio between regular field and turbulent field $B_r/B_t$ (bottom panel). The distance is fixed at 1 kpc. The dashed line in the histogram mark the average value of the separation.
  • Figure 3: Scatter plot of offsets and total counts of the identified source which is closest to the accelerator for different $L_c$ (top panels), $B^2$ (middle panels), and $B_r/B_t$ (bottom panels). The distance is fixed at 6 kpc (the pixel size 0.1$^\circ$ corresponding to $\approx 10$ pc; the PSF ( 0.3$^\circ$) corresponding to $\approx 30$ pc). In the left columns, the luminosity is $\mathcal{L}=\mathcal{L}_{\rm ref}$, while in the right columns, the luminosity is $\mathcal{L}=10\mathcal{L}_{\rm ref}$. Dashed lines in the histogram mark the average value of the offset.