Observation of Solar Neutron Decay Protons by the International Solar Neutron Detection Network

Possibly, in association with a large solar flare on May 27th of 2024 (start time 06:57UT), the solar neutron detector located at Mt. Chacaltaya (5,250m a.s.l.) detected an enhancement with 11.5 sigma in the counting rate. Taking into account the local time of Bolivia (~4 a.m.), this enhancement was possibly induced by solar neutron decay protons (SNDPs). To support this assumption, we simulated the trajectory of such protons by ejecting anti-protons with the energy of 10 GeV from 20 km above the observation site and investigated the penetration points on a sphere with radius of 10 Re. The results show that these anti-protons came from the day-side of the Earth. Furthermore we searched for signals in other stations, Jungfraujoch, Mexico city (both neutron monitors), and Mt. Aragats (solar neutron detector). All detectors located at these stations recorded enhancements with 3.4~6.7 sigma. An excess signal was also recorded in the SOHO/EPHIN detector that may support the hypothesis that solar neutron decay electrons and protons were produced in association with this solar flare. Therefore, we have another evidence that the May 27, 2024 event may be counted as the 6th event of Solar Neutron Decay Protons in the history of solar cosmic ray research. Furthermore this event may be pointed out as the second event of Neutron GLE following May 24th 1990 event.