Understanding the graph of cosmic rays flux This graph is to be found in various Articles, Papers, and websites.

I am trying to understand, what the "y axis" represent.
Are they refering to electromagnetic Flux ? What is this unit being used ? (m^2 , Sr, s Gev)^-1
Furthermore, what is meant by 1 Particle per m^2 sec\year, so on?
Thank you
 A: This graph shows the distribution of cosmic rays detected on ground (per unit of time [s], surface [m$^2$], energy [GeV] and solid angle ["sr", i.e. steradian]), with respect to their energy [eV].
It is not an electromagnetic flux, but a particle flux. Cosmic rays are not photons, they are high-energy particles traveling through space (hadrons, leptons; for example protons and electrons, etc.)
You can read the graph as follows : on Earth, the incoming flux of cosmic rays with an energy $E= 10^{19}$ eV is approximately $10^{-24}$ m$^{-2}$ sr$^{-1}$ s$^{-1}$ GeV$^{-1}$. It means that on a 1 kilometer surface, it would require (statistically) :
$ 1  ~ / ~ (10^6 \mathrm{[m \rightarrow km~surface]} \times 10^{19} \mathrm{[particle~energy, "x~axis"]} \times 10^{-24} \mathrm{[flux, "y~axis"]} \times 10^{-9} \mathrm{[eV \rightarrow GeV]} \times 2\pi \mathrm{[full~hemisphere~coverage]}) = 10^{8} / 2 \pi~\mathrm{seconds}$
to observe one cosmic ray with that energy, or approximately 6 months.
By the way, this is why the errorbars are larger at the bottom-right end of the graph. These high-energy events are very rare.
