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 gamma-ray point sources. We examine the implications of the recent Milagro gamma-ray Observatory detection of extended, multi-TeV gamma-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 gamma-ray and electron or positron experiments (up to approximately 100 TeV) that can confirm the first "direct" detection of a cosmic-ray source.