Geminga contribution to the cosmic-ray positron excess according to the gamma-ray observations |
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Authors: | Guang-Yao Zhou Zhao-Huan Yu Qiang Yuan Hong-Hao Zhang |
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Institution: | 1.School of Physics, Sun Yat-Sen University, Guangzhou 510275, China;2.Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, China;3.School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, China |
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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 γ rays via inverse Compton scattering, we take into account the extended γ-ray observations around Geminga from HAWC for ∼10 TeV and from Fermi-LAT for ${ \mathcal O }(10)$ GeV. According to the extended γ-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 γ rays given by another Fermi-LAT analysis, positrons from Geminga would be insufficient to account for the positron excess. Further robust analysis of Fermi-LAT data for the extended γ rays would be crucial to determine whether Geminga can explain the positron excess or not. |
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Keywords: | pulsar cosmic rays gamma rays |
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