TITLE:   GCN CIRCULAR
NUMBER:  14503
SUBJECT: GRB 130427A in the Ep,i - Eiso plane
DATE:    13/04/29 17:09:35 GMT
FROM:    Lorenzo Amati at INAF-IASF/Bologna  <amati@iasfbo.inaf.it>

L. Amati (INAF - IASF Bologna, Italy), S. Dichiara, F. Frontera, C. 
Guidorzi (University of Ferrara, Italy), report:

Based on the preliminary values of fluence and spectral parameters 
reported by the Fermi/GBM (Kienlin et al., GCN 14473) and Konus-Wind 
(Golenetskii et al., GCN 14487) teams, and by assuming a redshift of 0.34 
(Levan et al., CGN 14455; Flores et al., GCN 14491) and a standard 
Lambda_CDM cosmology with H_0 = 70 km/s/Mpc, Omega_M = 0.27, Omega_Lambda 
= 0.73, we estimate for GRB 130427A an intrinsic spectral peak energy Ep,i 
of 1250+/-150 keV and an isotropic-equivalent radiated energy of 
(1.05+/-0.15)x10^54 erg (1-10000 keV cosmological rest-frame).

These values are fully consistent with the best-fit power-law of the 
Ep,i-Eiso correlation holding for all long-bright cosmological GRBs (as 
determined, e.g., by Amati et al. 2009, A&A 508, 173). This is further 
evidence that the prompt emission properties of GRB 130427A, the most 
energetic GRB detected at z < 1, are the same as those of very bright, 
high-redshift events. Hence, its relatively low redshift makes it a unique 
case for investigating wether this class of events is associated to SNe 
with properties similar to those associated to "local" sub-luminous GRBs.