Gamma ray burst triggers at daytime and night-time interface

TL;DR

This paper investigates gamma ray burst triggers coinciding with sunset-related ionospheric phenomena in the South Atlantic Anomaly, suggesting some triggers are caused by particle precipitation during sunset enhancement.

Contribution

It presents observational evidence linking gamma ray burst triggers with ionospheric sunset enhancement effects in the SAA region, highlighting possible noise triggers from particle precipitation.

Findings

Five GRB triggers coincided with sunset enhancement periods.

Some triggers are likely noise caused by particle precipitation.

Ground and space observations support ionospheric influence on triggers.

Abstract

There is a difference between the solar ionization concentration in the ionosphere in the daytime and at night-time. At night the E-region ion concentration peak is dramatically reduced due to chemical losses and the rapid change in the vertical polarization electric field at the time around sunset, which is due to the accelerating neutral wind dynamo and which produces a corresponding change in the zonal electric field through curl-free requirements. The result is the formation of a layer of high conductivity, at the daytime-night-time interface. This phenomenon in the South Atlantic Anomaly (SAA) area, provokes an increase in the precipitation of charge particles which is well known and is commonly termed "sunset enhancement". In the following we show five gamma ray burst (GRB) triggers observed by spacecraft GRB detectors in temporal coincidence with muon enhancement observed at ground level by the Tupi telescopes with two different orientations at $\sim 21$ UT (local sunset), and located inside the SAA region. Of these GRB triggers analyzed here, one from Swift, and two from Fermi are probably noise triggers, produced by omni-directional particle precipitation, during the sunset enhancements.