It is the force-field approximation, the simple standard formula (no solution of Parker equation).
It is better to make the plots yourself since then you know exactly what is done.
This quick plot utility is not intended to be publication quality.
Note that the force-field approximation is known to be invalid (e.g. does not include charge-dependence),
but is just a convenient way to parameterize the spectrum.
Recent work worth looking at is http://arxiv.org/abs/1211.6905
If you need more help I can provide some more details on how to apply the force-field (even though its use is problematic).
You may also be interested in recent work using gamma rays which shows the modulation directly without any model, slide 7 of thishttp://www.mpe.mpg.de/~aws/talks/strong ... online.pdf