Neutrinos? (from the wikipedia page).
I don't think it's totally ridiculous to assume that different particles with different magnetic moments were affected differently by the immense magnetic field of a magnetar. But if the Gamma, Xray, and radio waves arrive within seconds of each other, it's hard to imagine another particle could've made the trip 1.5 days quicker. But maybe that's just my lack of imagination and poor math skills.