Search for a simultaneous signal from small transient events in the Pierre Auger Observatory and the Tupi muon telescopes

TL;DR

This study searches for correlated signals of small transient solar events and gamma-ray bursts using the Tupi muon telescope and Pierre Auger Observatory, finding potential ground-level muon enhancements associated with a specific GRB.

Contribution

It presents the first simultaneous analysis of small solar transient events and GRB counterparts using two ground-based cosmic ray detectors located in the South Atlantic Anomaly.

Findings

Detection of an 8 sigma muon enhancement coincident with GRB 110928B

Observation of solar activity-related variations in low-energy particle counts

Potential ground-level signature of a long-duration GRB

Abstract

We present results of a search for a possible signal from small scale solar transient events (such as flares and interplanetary shocks) as well as possible counterparts to Gamma-Ray Burst (GRB) observed simultaneously by the Tupi muon telescope Niteroi-Brazil, 22.90S, 43.20W, 3 m above sea level) and the Pierre Auger Observatory surface detectors (Malargue-Argentina, 69.30S, 35.30W, altitude 1400 m). Both cosmic ray experiments are located inside the South Atlantic Anomaly (SAA) region. Our analysis of several examples shows similarities in the behavior of the counting rate of low energy (above 100 MeV) particles in association with the solar activity (solar flares and interplanetary shocks). We also report an observation by the Tupi experiment of the enhancement of muons at ground level with a significance higher than 8 sigma in the 1-sec binning counting rate (raw data) in close time coincidence (T-184 sec) with the Swift-BAT GRB110928B (trigger=504307). The GRB 110928B coordinates are in the field of view of the vertical Tupi telescope, and the burst was close to the MAXI source J1836-194. The 5-min muon counting rate in the vertical Tupi telescope as well as publicly available data from Auger (15 minutes averages of the scaler rates) show small peaks above the background fluctuations at the time following the Swift-BAT GRB 110928B trigger. In accordance with the long duration trigger, this signal can possibly suggest a long GRB, with a precursor narrow peak at T-184 sec.