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Frascati Workshop 2007: Multifrequency Behaviour of High Energy Cosmic Sources, Vulcano : Italie (2007)
The afterglow onset for GRB060418 and GRB060607A
S. Covino, S.D. Vergani, D. Malesani, E. Molinari, P. D'Avanzo, G. Chincarini, F.M. Zerbi, L.A. Antonelli, P. Conconi, V. Testa, G. Tosti, F. Vitali, F. D'Alessio, G. Malaspina, L. Nicastro, E. Palazzi, D. Guetta, S. Campana, P. Goldoni1, 2, N. Masetti, E.J.A. Meurs, Alessandro Monfardini3, L. Norci, E. Pian, S. Piranomonte, D. Rizzuto, M. Stefanon, L. Stella, G. Tagliaferri, P. A. Ward, G. Ihle, L. Gonzalez, A. Pizarro, P. Sinclair, J. Valenzuela

Gamma-ray burst are thought to be produced by highly relativistic outflows. Although upper and lower limits for the outflow initial Lorentz factor γ_0 are available, observational efforts to derive a direct determination of γ_0 have so far failed or provided ambiguous results. As a matter of fact, the shape of the early-time afterglow light curve is strongly sensitive on γ_0 which determines the time of the afterglow peak, i.e. when the outflow and the shocked circumburst material share a comparable amount of energy. We now comment early-time observations of the near-infrared afterglows of GRB 060418 and GRB 060607A performed by the REM robotic telescope. For both events, the afterglow peak was singled out and allowed us to determine the initial fireball Lorentz, γ_0~400.
1 :  APC - UMR 7164 - AstroParticule et Cosmologie
2 :  DAPNIA - Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée
3 :  NEEL - Institut Néel
Physique/Astrophysique/Cosmologie et astrophysique extra-galactique

Planète et Univers/Astrophysique/Cosmologie et astrophysique extra-galactique

Planète et Univers/Astrophysique
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