Muon enhancements at sea level in association with Swift-BAT and MILAGRO triggers

Abstract

Recently, triggers occurring during high background rate intervals have been reporter by the Swift-BAT gamma-ray burst detector. Among them, there were two on January 24, two on January 25, and two on February 13 and 18, all in 2008. These Swift-BAT triggers in most cases are probably noise triggers that occurred while Swift was entering the South Atlantic Anomaly (SAA). In fact, we show that they happen during a plentiful precipitation of high energy particles in the SAA, producing muons in the atmosphere detected by two directional telescopes at sea level, inside the SAA region (Tupi experiment). They look like sharp peaks in the muon counting rate. In the same category are two triggers from the MILAGRO ground-based detector, on January 25 and 31, 2008, respectively. In addition, the trigger coordinates are close to (and, in two cases, inside) the field of view of the telescopes. From an additional analysis in the behavior of the muon counting rate, it is possible to conclude that the events are produced by precipitation of high energy charged particles in the SAA region. Thus, due to its localization, the Tupi experiment constitutes a new sensor of high energy particle precipitation in the SAA, and it can be useful in the identification of some triggers of gamma-ray burst detectors.