Supernova origin of cosmic rays from a gamma-ray signal in the Constellation III region of the Large Magellanic Cloud

Abstract

Cosmic rays could be produced via shock acceleration powered by supernovae. The supernova hypothesis implies that each supernova injects on average some 1e50 erg in cosmic rays, while the shock acceleration model predicts a powerlaw cosmic ray spectrum with the slope close to 2. Verification of these predictions requires measurements of spectrum and power of cosmic ray injection from supernova population(s). Here we obtain such measurements based on gamma-ray observation of Constellation III region of Large Magellanic Cloud. We show that gamma-ray emission from this young star formation region originates from cosmic rays injected by approximately two thousand supernovae, rather than by massive star wind powered superbubble pre-dating supernova activity. Cosmic ray injection power is found to be (1.1-0.2+0.5)x 1e50 erg/supernova (for the estimated interstellar medium density 0.3/cm3). The spectrum is a powerlaw with slope 2.09-0.07+0.06. This agrees with the model of particle acceleration at supernova shocks and provides a direct proof of the supernova origin of cosmic rays.