John W. BieberJohn ClemPaul EvensonRoger PyleDavid RuffoloAlejandro SáizBartol Research InstituteMahidol UniversityChulalongkorn University2018-06-212018-06-212005-02-16Geophysical Research Letters. Vol.32, No.3 (2005), 1-5009482762-s2.0-17744387711https://repository.li.mahidol.ac.th/handle/20.500.14594/16493The 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. Copyright 2005 by the American Geophysical Union.Mahidol UniversityEarth and Planetary SciencesArticleSCOPUS10.1029/2004GL021492