Misidentification of the source of a neutron transient detected by MESSENGER on 4 June 2011

AbstractLow‐energy (1–10 MeV) neutrons emanating from the Sun provide unique information about accelerated ions with steep energy spectra that may be produced in weak solar flares. However, observation of these solar neutrons can only be made in the inner heliosphere where measurement is difficult due to high background rates from neutrons produced by energetic ions interacting in the spacecraft. These ions can be from solar energetic particle events or produced in passing shocks associated with fast coronal mass ejections. Therefore, it is of the utmost importance that investigators rule out these secondary neutrons before making claims about detecting neutrons from the Sun. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) neutron spectrometer recorded an hour‐long neutron transient beginning at 15:45 UTC on 4 June 2011 for which Lawrence et al. (2014) claim there is “strong evidence” that the neutrons were produced by the interaction of ions in the solar atmosphere. We studied this event in detail using data from the MESSENGER neutron spectrometer, gamma ray spectrometer, X‐ray Spectrometer, and Energetic Particle Spectrometer and from the particle spectrometers on STEREO A. We demonstrate that the transient neutrons were secondaries produced by energetic ions, probably accelerated by a passing shock, that interacted in the spacecraft. We also identify significant faults with the authors' arguments in favor of a solar neutron origin for the transient.