Relativistic solar neutrons and protons on 28 October 2003

The solar cosmic ray event associated with the X17.2 class flare of 28 October 2003 was unusual in several respects: (1) Several high‐latitude neutron monitors observed a large, highly anisotropic spike at event onset. (2) The earliest onset was detected by stations viewing towards the anti‐Sunward hemisphere. (3) The event displayed an extremely slow, protracted decay. (4) The near‐equatorial monitor in Tsumeb, Africa recorded a small increase consistent with a solar neutron event ≈7 minutes prior to the onset at high latitudes. We analyze these signals and infer that relativistic solar neutrons were emitted over a duration of ≈9 minutes, starting ≈7 minutes before the main injection of relativistic protons.