The TeV Cosmic-Ray Bump: A Message from the Epsilon Indi or Epsilon Eridani Star?

Area of Science:

• Astrophysics
• Cosmic Ray Physics

Background:

• A distinct bump in the cosmic-ray (CR) spectrum between 0.3 and 30 TV has been observed.
• This spectral feature is hypothesized to originate from astrophysical sources influencing CR propagation.
• Previous models required numerous parameters to fit the observed CR spectrum bump.

Purpose of the Study:

• To propose and validate a physical model for the observed cosmic-ray spectral bump.
• To identify potential stellar sources responsible for reaccelerating cosmic rays.
• To investigate the role of Iroshnikov-Kraichnan turbulence in CR propagation.

Main Methods:

• Developed a model based on stellar bow shocks reaccelerating pre-existing CRs.
• Incorporated Iroshnikov-Kraichnan (I-K) turbulence to explain CR propagation and bump sustainment.
• Constrained the model using three physical parameters: shock Mach number (M), size (l⊥), and distance (ζobs).

Main Results:

• The model accurately fits the observed CR spectral bump (≈0.08% accuracy) using only three physical parameters.
• The derived parameters (M ≈ 1.5-1.6, R0 ≈ 4.4 TV) strongly support the I-K turbulence spectrum.
• A distance-size relation for the shock was established: ζobs(pc) ~ 10^2 * sqrt(l⊥(pc)).
• Potential sources like Scholz's Star, Epsilon Indi, and Epsilon Eridani were identified at distances of 3-10 pc.

Conclusions:

• The model provides a physically grounded explanation for the cosmic-ray spectral bump, ruling out alternative explanations.
• Epsilon Indi and Epsilon Eridani are proposed as likely sources based on their proximity and characteristics.
• The proximity of these stars suggests the CR bump's appearance may evolve over relatively short timescales.