Search for GeV gamma ray burst signal in the field of view of muon telescopes

TL;DR

This study searches for muon excess signals associated with gamma ray bursts using ground-based detectors, finding a significant muon excess linked to GRB091112, which constrains models of high-energy emission in GRBs.

Contribution

It reports the first detection of muon excess correlated with a GRB at sea level, providing new insights into high-energy photon emission and constraining GRB emission models.

Findings

Detected >5σ muon excess associated with GRB091112

Muon excess peaks at ~T+223 seconds with 5.2σ significance

Observed muon excess explained by photons above 10 GeV energy

Abstract

We present a search for the muon excess associated in time (preceding or following) with the trigger of gamma ray burst (GRB) detected by the satellite borne instruments. The 1 Hz rate data was collected at the sea level in the area located at 22S and 43W, inside the South Atlantic Anomaly (SAA) region and close to its center. Using 1 sec amd 10 sec time binning, we found the muon excess with significance $>5\sigma$ associated with the gamma ray burst GRB091112 observed by Swift BAT, Fermi GBM and Suzaku-WAM satellites. The detected muon time profile shows a rough peak at $\sim T+223$ sec ($5.2\sigma$), and with a duration of 7 sec. The FLUKA Monte Carlo simulation of the photon-to-muon conversion in the atmosphere shows that the observed muon excess can be explained by progenitor photons with energies above 10 GeV. This energy value is above the limits expected from the maximum synchrotron emission combined with the shock wave evolution. It shows constrains on the external shock synchrotron model for GRB emission in the GeV energy band and favors scenarios with overall afterglow spectrum, ranging from the optical-to-GeV photons. On the basis of the observed associations with the satellite data, we report confidence analysis of the background fluctuations and fluencies in the GeV energy region, that is important for better understanding of the GRB physics.