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

TL;DR

A number of testable predictions for gamma-ray and electron or positron experiments (up to approximately 100 TeV) are explored that can confirm the first "direct" detection of a cosmic-ray source.

Abstract

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.

Figures (3)

• Figure 1: The cosmic-ray positron fraction. Shown are data compiled from Refs. Beatty:2004cyAdriani:2008zrAguilar:2007yfclempriv:2008, and scenarios based on the secondary model of Ref. Moskalenko:1997gh (shaded) and a plausible Geminga contribution (solid, dashed, and dotted lines) dependent upon distance and energetics (see text for details).
• Figure 2: Minimal inverse-Compton gamma-ray spectrum of the extended emission from Geminga (shaded) and the Milagro measurement at 20 TeV ( left axis). Also, the energy distribution (dotted line) of the associated $e^\pm$ ( right axis).
• Figure 3: Cosmic-ray $e^- + e^+$ data from Fermi Fermi:2009zk, HESS Aharonian:2008aaaAharonian:2009ah, and Refs. Torii:2008xuChang:2008zzr and AMS $e^-$-only data Aguilar:2007yf; with Galactic $e^-$ model modified from Ref. Moskalenko:1997gh (solid), contributions from Geminga (lower lines), and total (upper lines).