Synchrotron Spectrum

What you are seeing: a single electron radiates a humped spectrum peaked at $\nu_c \propto \gamma^2 B$ . A power-law electron distribution $N(\gamma) \propto \gamma^{-p}$ produces a power-law photon spectrum $F_\nu \propto \nu^{-(p-1)/2}$ .

Figure 1. Single-electron hump and power-law ensemble.

γ2000

log10(B / G)-4.00

p (power law)2.40

mode

WHAT TO TRY

Switch to a single electron: it radiates a humped spectrum peaking at the critical frequency, proportional to gamma squared times B, so faster electrons and stronger fields push the peak up.
Switch to a power-law ensemble: summing electrons with N(gamma) ~ gamma^-p gives a power-law spectrum of slope (p-1)/2, the fingerprint read off radio jets and supernova remnants.
Crank B or gamma and the whole spectrum shifts up: the same physics that makes pulsar wind nebulae glow all the way from radio to gamma rays.