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

Understand

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 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/positron experiments (up to ~100 TeV) that can confirm the first "direct" detection of a cosmic-ray source.