Detection of a $\gamma$-ray halo around Geminga with the Fermi-LAT and implications for the positron flux

Understand

The HAWC Collaboration has discovered a $\gamma$-ray emission extended about 2 degrees around the Geminga and Monogem pulsar wind nebulae (PWNe) at $\gamma$-ray energies $E_\gamma >5$ TeV.

• We analyze, for the first time, almost 10 years of $\gamma$-ray data obtained with the Fermi Large Area Telescope at $E_\gamma >$ 8 GeV in the direction of Geminga and Monogem.
• Since these two pulsars are close the Galactic plane we run our analysis with 10 different interstellar emission models (IEMs) to study the systematics due to the modeling of this component.
• We detect a $\gamma$-ray halo around Geminga with a significance in the range $7.8-11.8\sigma$ depending on the IEM considered.