Geminga contribution to the cosmic-ray positron excess according to the gamma-ray observations

TL;DR

This paper investigates whether the nearby pulsar Geminga can explain the observed cosmic-ray positron excess by analyzing gamma-ray observations and considering different data interpretations, highlighting the importance of further gamma-ray data analysis.

Contribution

It introduces a two-zone diffusion model with a low energy cutoff for Geminga's injection spectrum and assesses its ability to explain the positron excess based on gamma-ray observations.

Findings

Geminga could explain the positron excess with 30% energy conversion efficiency.

Alternative gamma-ray constraints suggest Geminga's contribution may be insufficient.

Further gamma-ray data analysis is needed to clarify Geminga's role.

Abstract

We attempt to interpret the cosmic-ray positron excess by injection from the nearby pulsar Geminga, assuming a two-zone diffusion scenario and an injection spectrum with a low energy cutoff. Since the high energy positrons and electrons from Geminga can induce $\gamma$ rays via inverse Compton scattering, we take into account the extended $\gamma$-ray observations around Geminga from HAWC for $\sim 10$ TeV and from Fermi-LAT for $\mathcal{O}(10)$ GeV. According to the extended $\gamma$-ray observation claimed by an analysis of Fermi-LAT data, we find that Geminga could explain the positron excess for a $30\%$ energy conversion efficiency into positrons and electrons. However, based on the constraint on the extended $\gamma$ rays given by another Fermi-LAT analysis, positrons from Geminga would be insufficient to account for the positron excess. A further robust analysis of Fermi-LAT data for the extended $\gamma$ rays would be crucial to determine whether Geminga can explain the positron excess or not.