V. Heussaff, J-L. Atteia, Y. Zolnierowski
We use a sample of GRBs detected by Fermi to analyze the correlation discovered by Amati et al. (2002) between Epi, the peak energy of the prompt GRB emission, and Eiso, the energy released by the GRB assuming isotropic emission. This correlation has been disputed by various authors, and our aim is to assess whether it is an intrinsic GRB property or the consequence of selection effects. We construct a sample of Fermi GRBs with homogeneous selection criteria, and study their distribution in the Epi-Eiso plane. Our sample is made of 43 GRBs with a redshift and 243 without. We show that GRBs with a redshift follow a broad Epi-Eiso relation, while GRBs without a redshift show several outliers. We use these samples to discuss the impact of selection effects associated with GRB detection and with redshift measurement. We find that the Epi-Eiso relation is partly due to intrinsic GRB properties and partly due to selection effects. The lower-right boundary of the Epi-Eiso relation is due to a true lack of luminous GRBs with low Epi. On the contrary, the upper left boundary is attributed to selection effects acting against the detection GRBs with low Eiso and large Epi, which appear to have lower signal-to-noise ratio. We also demonstrate that GRBs with and without a redshift follow different distributions in the Epi-Eiso plane. GRBs with a redshift are concentrated near the lower-right boundary of the Epi-Eiso relation. This suggests that it is easier to measure the redshift of GRBs close to the lower Epi-Eiso boudary, and that GRBs with a redshift follow the Amati relation better than the general population. We attribute the controversy about the reality of the Amati relation to the complex nature of this relation, which results from the combination of a true physical boundary and biases favoring the detection and the measurement of the redshift of GRBs located close to this boundary.
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http://arxiv.org/abs/1306.1757
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