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 1-sigma 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 constraining the redshift meaningfully. Hence, the Eiso-Epeak relation is not useful for determining the GRB distance.

4 pages, 4 figures. Accepted by MNRAS Letters

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• Are GRB 980425 and GRB 031203 real outliers or twins of GRB 060218?
• The soft X-ray blast in the apparently sub-luminous GRB 031203

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