Journal of the Korean Physical Society

pISSN 0374-4884 eISSN 1976-8524

Article

Published online May 14, 2010     https://doi.org/10.3938/jkps.56.1598

Copyright © The Korean Physical Society.

GRB early afterglow observations with the REM robotic telescope

Susanna Diana Vergani, Stefano Covino, Daniele Malesani, Cristiano Guidorzi, Paolo D'Avanzo, Eliana Palazzi

J. Korean Phys. Soc. 56(5(1)), 1598 - 1602 (2010)

Abstract

Gamma-ray burst are thought to be produced by highly relativistic outflows. Althoughupper and lower limits for the outflow initial Lorentz factor $Gamma_0$ are available, observationalefforts to derive a direct determination of $Gamma_0$ have so far failed or provided ambiguousresults. As a matter of fact, the shape of the early-time afterglow light curve is strongly sensitive on $Gamma_0$which determines the time of the afterglow peak, i.e. when the outflow and the shocked circumburstmaterial share a comparable amount of energy.We now comment early-time observations of the near-infrared afterglows of GRB,060418 and GRB,060607Aperformed by the REM robotic telescope.For both events, the afterglow peak was singled out and allowed us to determine the initial fireball Lorentz,$Gamma_0sim400$.