How well can a cosmic-ray spectral kink be measured? Original Research Article

The spectrum of cosmic rays follows a power law with index around 2.7 for energies below 1014 eV, but it is considerably steeper for energies above 5 × 1015 eV. This suggests that more than one astrophysical process may be responsible for cosmic ray acceleration. Theoretical arguments based on supernovae shock acceleration suggest a maximum attainable energy of approximately Z × 1014 eV. There is no general consensus for the source of cosmic ray acceleration beyond this energy. In order to better understand the physics of acceleration, it is imperative to measure separately the spectrum of each cosmic ray component and to determine accurately the “knee” in the spectrum. How well the spectral change can be measured depends on the characteristic of the spectral break and the performance of the measuring instrument. The former includes how sharp the break is at the to-be-determined kink energy. The latter includes the energy resolution and its energy dependence, as well as the charge resolution, which is affected by both the backscatter rejection power and the trajectory resolution. Here we discuss the constraints that the finite energy resolution and finite statistics impose on our ability to resolve the spectral break and to measure accurately the kink energy.