TITLE: GCN CIRCULAR NUMBER: 14576 SUBJECT: GRB 130505A: Largest E_iso ever measured DATE: 13/05/05 20:03:36 GMT FROM: Alexander Kann at TLS Tautenburg D. A. Kann (TLS Tautenburg), and S. Schulze (PUC, MCSS) report: Using the energetics provided by the Konus-Wind detection (Golenetskii et al. 2013, GCN 14575) of the extremely intense Swift GRB 130505A (Cannizzo et al. 2013, GCN 14564), and employing k-correction (Bloom et al. 2003, ApJ, 594, 674), we determine the isotropic energy release in the bolometric band (rest-frame 1 keV - 10 MeV) to be (5.65 +/- 0.13) x 10^54 erg (log E_iso = 54.75 +/- 0.01). The most isotropically energetic GRBs known so far (all in the rest-frame bolometric band) are GRBs 990123, 080916C and 090323, for which log E_iso ~ 54.5 - 54.6 has been found (e.g., Kann et al. 2010, ApJ, 720, 1513). This makes GRB 130505A the most energetic GRB known, and may indicate either an ultra-luminous event or a high degree of collimation. We additionally note that the nearby GRB 130427A (Maselli et al. 2013, GCN 14448; Golenetskii et al. 2013, GCN 14487) is also highly energetic, with log E_iso,bol = 54.21 +/- 0.05, but this is about 3.5 times less than GRB 130505A. This message may be cited.