Fermi Gamma-ray Space Telescope

GRB 130427A in Cosmological Context

Daniel Kocevski
Judith Racusin on behalf of the Fermi LAT collaboration

Abstract:

The observations of GRB 130427A by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope has provided a wealth of new data with which to study these unique transient events. GRB 130427A was exceptional in its observer frame properties, being among the highest fluence bursts ever detected. Here we show that although GRB 130427A exhibited an extremely high observed energy fluence in both gamma-ray and X-ray energies, its rest frame Eiso and X-ray luminosity, while large, are comparable to other LAT detected GRBs. Through simulations, we show that GRB 130427A would likely have been detected out to redshift ~ 4-5, but that the observed GeV emission would have become undetectable by the LAT beyond redshift ~ 2. This implies that the extra-ordinary extended GeV emission observed from this burst could be ubiquitous in the LAT detected population of GRBs and that selection effects play an important role in limiting our knowledge of their intrinsic properties at high energies. We speculate on the importance of these results on future stacked searches for neutrino signals from long GRBs.