The summary (and linked article) do a poor job of explaining the process and imply some change in the speed of light (there isn't one). The problem with the article (http://arxiv.org/abs/1111.6986) is that it ignores a bunch of more relevant data: Fermi-LAT observed photons from the same GRB over a very wide energy range placing an extremely good limit on effects like this proposed in the article (http://arxiv.org/abs/1305.3463).
Furthermore this is NOT new; the original article was posted in 2011 and only recently published in the "New Journal of Physics" which has apparently only published 16 volumes and I believe has had its email permanently redirected to my spam box.
Finally why do people link to Medium and not the actual article for physic related news items? We have demanded open, free access to all our papers since the birth of the internet (I speak as a physicist). Do everyone a favor and find the arxiv link and include it in your summary when submitting physics stories to Slashdot.
I have hardly ever known a mathematician who was capable of reasoning. -- Plato