Not necessarily. Particles will all be charged plasma and it is possible that those will be deflected by magnetic fields. But I am not astrophysicist so you wou

Not necessarily. Particles will all be charged plasma and it is possible that those will be deflected by magnetic fields. But I am not astrophysicist so you would want to check on it. Also, in contrast with the flash where all light has the same speed, the particles will have different speed so it will all be smeared in time (read -- much smaller in amplitude and hard to detect) and arriving much later than the flash. Then from the point of view of observer on Earth surface, charged particles will not be coming exactly from the source but at a bit of an angle (due to magnetic fields present). Again, I have no knowledge about the magnitude of the effect and I also suspect that the people who know this shit have some way to account for it...