Limits on the GeV Emission from Gamma-Ray Bursts

Understand

The Large Area Telescope (LAT) on board of the Fermi satellite detected emission above 30 MeV only in a small fraction of the long gamma-ray bursts (GRBs) detected by the Fermi Gamma-ray Burst Monitor (GBM) at 8 keV - 10 MeV.

• Those bursts that were detected by the LAT were among the brightest GBM bursts.
• We examine a sample of the most luminous GBM bursts with no LAT detection and obtain upper limits on their high energy fluence.
• We find an average upper limit of LAT/GBM fluence ratio of 0.13 for GeV fluence during $T_{90}$ and an average upper limit ratio of 0.45 for GeV fluence during the first 600 seconds after the trigger.