Signature of Energy Losses on the Cosmic Ray Electron Spectrum

Area of Science:

• Astrophysics
• Particle Physics
• Cosmic Ray Physics

Background:

• The precise origin and behavior of cosmic rays are key areas of research.
• Observed anomalies in cosmic ray electron spectra, such as the AMS-02 excess, have prompted various theoretical explanations.
• Understanding energy loss mechanisms is crucial for interpreting cosmic ray data.

Purpose of the Study:

• To investigate the origin of the fine structure in the cosmic ray electron spectrum, particularly the AMS-02 excess.
• To determine if observed spectral features can be explained by known astrophysical processes.
• To constrain models of cosmic ray transport and energy loss.

Main Methods:

• Analysis of cosmic ray electron spectrum data, focusing on energies above 42 GeV.
• Modeling of energy losses, including inverse Compton scattering on background photons (UV, IR, CMB) and synchrotron radiation in the Galactic magnetic field.
• Comparison of model predictions with observational data to identify the dominant physical processes.

Main Results:

• The observed fine structure in the cosmic ray electron spectrum, including the AMS-02 excess, is fully explained by inverse Compton and synchrotron energy losses.
• The transition to the Klein-Nishina regime on the ultraviolet photon background is identified as the cause of the spectral feature.
• The findings indicate that the observed spectral feature is distinct from the positron excess and does not necessitate the overlap of multiple cosmic ray components.

Conclusions:

• The electron spectrum anomaly is a consequence of energy losses, not new particle sources.
• Cosmic ray lepton transport in the Galaxy is confirmed to be loss-dominated down to tens of GeV.
• This conclusion places significant constraints on alternative cosmic transport theories that propose late-stage energy loss dominance.