Authors
E Molinari, Susanna D Vergani, D Malesani, S Covino, P d'Avanzo, G Chincarini, FM Zerbi, LA Antonelli, P Conconi, V Testa, Gino Tosti, F Vitali, F d'Alessio, G Malaspina, L Nicastro, E Palazzi, D Guetta, S Campana, P Goldoni, N Masetti, EJA Meurs, Alessandro Monfardini, Laura Norci, E Pian, S Piranomonte, D Rizzuto, M Stefanon, L Stella, G Tagliaferri, PA Ward, G Ihle, L Gonzalez, A Pizarro, P Sinclaire, J Valenzuela
Publication date
2007/7/1
Journal
Astronomy & Astrophysics
Volume
469
Issue
1
Pages
L13-L16
Publisher
EDP Sciences
Description
Context
Gamma-ray burst (GRB) emission is believed to originate in highly relativistic fireballs.
Aims
Currently, only lower limits were securely set to the initial fireball Lorentz factor . We aim to provide a direct measure of .
Methods
The early-time afterglow light curve carries information about , which determines the time of the afterglow peak. We have obtained early observations of the near-infrared afterglows of GRB 060418 and GRB 060607A with the REM robotic telescope.
Results
For both events, the afterglow peak could be clearly singled out, allowing a firm determination of the fireball Lorentz of 400, fully confirming the highly relativistic nature of GRB fireballs. The deceleration radius was inferred to be 1017 cm. This is much larger than the internal shocks radius (believed to power the prompt emission), thus providing further evidence for a different origin of the prompt and afterglow stages of the GRB.
Total citations
Scholar articles
E Molinari, SD Vergani, D Malesani, S Covino… - Astronomy & Astrophysics, 2007