Origin of the positron excess in cosmic rays

Area of Science:

• Astrophysics
• Particle Physics
• Cosmic Ray Physics

Background:

• The PAMELA experiment detected an excess of positrons in cosmic rays, challenging standard models of cosmic ray origin.
• Positron excess suggests potential contributions from exotic sources like dark matter annihilation or pulsars.

Purpose of the Study:

• To investigate if the observed positron excess can be explained within the standard scenario of Galactic cosmic ray origin.
• To identify the physical mechanisms responsible for generating the positron excess from known astrophysical processes.

Main Methods:

• Modeling the production and propagation of secondary positrons within astrophysical sources.
• Simulating the acceleration process of charged particles, including secondary positrons, in supernova remnants.
• Analyzing the spectral properties of positrons after propagation through the Milky Way galaxy.

Main Results:

• The study demonstrates that secondary positrons produced within cosmic ray sources can naturally explain the observed positron excess.
• A key finding is that secondary positrons participate in the acceleration process, resulting in a very flat energy spectrum.
• The strength of this effect is dependent on environmental parameters during the late stages of supernova remnant evolution.

Conclusions:

• The standard scenario for Galactic cosmic ray origin, with secondary positron production and acceleration within sources, provides a natural explanation for the PAMELA positron excess.
• This mechanism offers a compelling alternative to exotic explanations for the observed positron excess.
• Further studies on supernova remnant evolution and environmental parameters are needed to refine the model.