Fermi Gamma-ray Space Telescope

Selection effects in the Epi-Eiso plane

V. Heussaff
J. L. Atteia, Y. Zolnierowski

Abstract:

The Epi-Eiso relation is one of the relations that has been proposed to standardize GRBs for cosmological purposes. Nevertheless, since the discovery of this relation, several studies have indicated that it could be affected by selection effects. For instance, while GRBs with a redshift seem follow this relation, this is not the case for GRBs without a redshift. Using the last Fermi/GBM catalog, we investigate the reality of selection effects in the Epi-Eiso plane. We highlight the existence of two selection effects which tend to prevent the detection of GRBs located above the Epi-Eiso relation. The first is connected with the difficulty to detect GRBs with low Eiso and large Epi, which radiate few gamma-ray photons. The second is related with the difficulty to have a redshift measurement for GRBs located above the Epi-Eiso relation due to optical afterglow fainter than other GRBs. We discuss the impact of these effects to shape the observed Epi-Eiso relation and to explain previous contradictory results.