Redshift degeneracy in the Eiso-Epeak relation of gamma-ray bursts

Abstract

In this Letter we show that there is a redshift degeneracy in the Eiso-Epeak relation of gamma-ray bursts (GRBs). If a GRB has a redshift solved from the Eiso-Epeak relation that lies in the range of 0.9 < z < 20, a GRB that has the same observed fluence and peak spectral energy but is at a different redshift in that range also satisfies the Eiso-Epeak relation within a 1σ error, implying an extremely large error in the calculated redshift. Even if the data scatter in the Eiso-Epeak relation is reduced by a factor of 2, the error in the predicted redshift is still large enough to prevent one from constraining the redshift meaningfully. Hence, the Eiso-Epeak relation is not useful for determining the GRB distance. © 2006 The Author. Journal compilation © 2006 RAS.