Chief, the x-ray flux graph is labeled misleadingly. Particle flux is always given as the number of received particles per second, per "window" of detection, where the window is normalized to an area (typically square centimeters) and to an incoming angle. Imagine baseballs thrown through your window. Your window has a given area -- square feet, or what have you. If a hooligan wants to throw a baseball through it, he'd have to stand reasonably in front of it -- i.e., within a certain solid angle. Otherwise he'd just see the window edge-on and couldn't throw his ball through it. The number of times he can do that per second is the flux. Obviously it's dependent on which way your window is facing. You can only count balls thrown from that direction.
Particle energy is like throwing a fast ball versus a softball lob. The faster he throws it, the more likely it is to break the glass. If he just tosses it underhand, it may just bounce off and have no adverse effect. Nature is like a hooligan who tires after a while. The vast majority of baseballs that fly into your window are softball lobs, which he can do until the cows come home. Fast balls take a lot of strength, so you won't get many of them. Similarly, in terms of electrons and protons from the sun, the vast majority of them are "slow pitch" particles. Only a few are zingers. So for science, it makes sense to measure the speed of the ball and keep a separate flux for lobs and fastballs. So at some given instant, particle flux is a graph of the rate at which particles of different energies are hitting the detector, so it looks like a graph with speed (which is particle energy in electron volts) on the x-axis and the number of hits for that energy as the y-axis.
X-rays are a little difficult because x-ray photons are harder to slice up that way. So the graph for x-ray "flux" isn't really a flux in the standard physics sense. The GOES detectors can't differentiate very well between "soft x-ray" photons (slow-pitch photons) and "hard x-ray" photons (slow-pitch). It really can only count how much broken glass is on the floor, so it counts up the total amount of energy in watts that's created by absorbing all the photons of all the different energies and graphs that instead.
