12: COSMIC RAY ORIGINS

Question 1

What do SN explosions and their remnants explain?

Answer 1

They have enough energy in high-energy particles to explain the population of CRs that originates in our Galaxy.

Question 2

What other evidence supports the idea that SNR contribute significantly to the cosmic ray population?

Answer 2

The gamma-ray emission has recently been detected from individual SNRs and the spectrum is found to be a good match from the gammas being produced from proton-proton collisions followed by pi-zero decay. This shows that protons in SNR are accelerated to the energies of observed CR protons.

Question 3

Other than highest energy CRs which are extragalactic in origin, what evidence from electrons shows CRs are of galactic origin?

Answer 3

1. Can’t be extragalactic - short lifetime against iC on CMB restricts to distances of nearest Galaxies
2. Spectral breaks fit well leaky-box model with leakage time ~ 10^7 years and p ~ 2.5
3. SNRs are a plausible source of enough energy (from synchrotron emission and minimum energy). Much harder to find enough total energy to fill the entire Universe with CRs.