Possible Detection of Gamma Ray Air Showers in Coincidence with BATSE Gamma Ray Bursts

Abstract

Project GRAND presents the results of a search for coincident high-energy gamma ray events in the direction and at the time of nine Gamma Ray Bursts (GRBs) detected by BATSE. A gamma ray has a non-negligible hadron production cross section; for each gamma ray of energy of 100 GeV, there are 0.015 muons which reach detection level (Fasso & Poirier, 1999). These muons are identified and their angles are measured in stations of eight planes of proportional wire chambers (PWCs). A 50 mm steel plate above the bottom pair of planes is used to distinguish muons from electrons. The mean angular resolution is 0.26 degrees over a +/- 61 degree range in the XZ and YZ planes. The BATSE GRB catalogue is examined for bursts which are near zenith for Project GRAND. The geometrical acceptance is calculated for each of these events. The product is then taken of the GRB flux and GRAND's geometrical acceptance. The nine sources with the best combination of detection efficiency and BATSE's intensity are selected to be examined in the data. The most significant detection of these nine sources is at a statistical significance of +3.7 sigma; this is also the GRB with the highest product of GRB flux and geometrical acceptance.