TeV Gamma Rays from Geminga and the Origin of the GeV Positron Excess

The Geminga pulsar has long been one of the most intriguing MeV-GeV γ-ray point sources. We examine the implications of the recent Milagro γ-ray Observatory detection of extended, multi-TeV γ-ray emission from Geminga, finding that this reveals the existence of an ancient, powerful cosmic-ray accelerator that can plausibly account for the multi-GeV positron excess that has evaded explanation. We explore a number of testable predictions for γ-ray and electron or positron experiments (up to ∼100TeV) that can confirm the first “direct” detection of a cosmic-ray source.