The E_p - E_iso relation: Intrinsic GRB property or/and selection effects?

Since its discovery the E_p - E_iso relation has been a source of controversy between those believing that it represents an intrinsic property of bursts that should be directly related to the physics of the prompt emission, and others arguing that it results from various selection effects (thresholds for burst and afterglow detection, for measuring the redshift, etc). In the context of the internal shock model we present a series of Monte-Carlo simulations showing that the observed relation may indeed come from a combination of intrinsic processes and selection effects. We find that the low E_p edge of the relation arises from the physics of shocks while the large E_p edge is mainly shaped by selection effects.