Not so fast (or maybe faster) Tom;
The work of Jenkins and Fischbach on varying rates of nuclear decay has resulted in an interesting development. Specifically; it was found there is a seasonal dependence where the rate of decay half-life varies measurably, with a cycle that appears to relate to Sun-Earth distance. But once a greater degree of precision was achieved, it was found that this variation is also observed during a Coronal Mass Ejection or CME.
My guess is that, because these events move a significant amount of mass in a very short time, this ripples or deforms the fabric of spacetime. So if there was a discrepancy between the scalar mode and tensor mode propagation, one would expect that arrival time for such a signal would be less than 8 minutes. This is apparently exactly what is observed. Now Professor Jenkins has a Patent pending for an Early Warning System for CME events - and he even appeared on the Weather Channel to talk about it.
A topological spacetime fabric is the simplest explanation, as light travels around, while gravity acts center to center, and the ripple is felt at the sub-atomic scale.
Regards,
Jonathan