Geminga: A Window into the Role Played by the Local Halo in the Cosmic-Ray Propagation Process

TL;DR

This paper investigates how the Geminga pulsar halo influences local cosmic-ray propagation, highlighting the importance of slow diffusion and proper motion in shaping observed gamma-ray and positron spectra.

Contribution

It introduces a 3D cosmic-ray propagation model incorporating Geminga, revealing its significant role in local cosmic-ray and gamma-ray observations.

Findings

Slow diffusion near Geminga affects radiation distribution.

Proper motion of Geminga influences halo extent.

Local halo radiation may contribute to gamma-ray fluctuations.

Abstract

A novel phenomenon among the recently observed Geminga pulsar halo is the presence of distinct radiation morphology at high energies, while no extended radiation is detected in the 10-500 GeV energy band within a $40\degree\times40\degree$ region. This phenomenon suggests that pulsar halos play a crucial role in the local propagation of cosmic rays, making it necessary to investigate the underlying mechanisms of this phenomenon. This work focuses on the 3D propagation study of cosmic rays, incorporating the Geminga pulsar into our propagation framework to investigate its contribution to different observational spectra. We consider Geminga a dominant local source of positrons, partially reproducing the observed positron spectrum and multi-wavelength radiative spectra of the Geminga halo. Through calculations of signal and background at different angles, we find that: (1) The slow-diffusion properties near the Geminga pulsar and its proper motion may cause the radiation from electrons originating from Geminga to be distributed across a more extended region. (2) The incomplete subtraction of radiation from the local halo may contribute, to some extent, to the diffuse gamma ray fluctuations detected by LHAASO. We hope that LHAASO will detect more sources of cosmic ray halo to further validate our model.