Interpretation of the puzzling gamma-ray spectrum of the Geminga halo

Abstract

The gamma-ray halo around Geminga is formed owing to the slow diffusion of the electrons released by the Geminga PWN. The latest HAWC and HESS observations exhibit complex features in the TeV gamma-ray spectrum of the Geminga halo. We first show that the new results cannot be interpreted by the commonly used simple model, where a single power-law injection spectrum and an energy index of $\delta =1/3$ for the diffusion coefficient are assumed. We then propose a two-population electron injection model based on the x-ray observations of the Geminga PWN, which consists of a population of freshly accelerated electrons escaping from the PWN through rapid outflows and a population trapped longer inside the PWN before escaping. The two-population model interprets the HAWC and HESS data well, and the goodness of fit improves significantly compared with the single power-law injection model. It also predicts a different energy dependency of the gamma-ray profile from the single power-law model, which could be tested by LHAASO in the coming future. We note that a $\delta$ slightly larger than 1 is needed to fit the HAWC and HESS data consistently. We also discuss the possible improvements by adopting the two-zone diffusion model.

15 pages, 4 figures

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Cited by in corpus (7)

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• Constraining the slow-diffusion zone size and electron injection spectral index for the Geminga pulsar halo
• Geminga contribution to the cosmic-ray positron excess according to the gamma-ray observations
• PHECT: A lightweight computation tool for pulsar halo emission
• The traveling-PWN modeling attempt on the enigmatic LHAASO dumbbell-like structure
• Pulsars as candidates of LHAASO sources J2226+6057, J1908+0621 and J1825-1326: The leptonic origin