GCN Circular 7682
Subject
GRB 080503: Slow-rise optical AG ?
Event
Date
2008-05-06T03:50:15Z (18 years ago)
From
Arnon Dar at Technion-Israel Inst. of Tech <arnon@physics.technion.ac.il>
Many long GRBs have optical light-curves which are initially slowly
rising. The optical light curve of the short hard burst (SHB) 080503 (Mao
et al. GCN 7665; Ukwatta et al. GCN 7673; Guidorzi et al. GCN 7674)
discovered by Perley et al. (GCNs 7678, 7680) may be their analog
slow-rise optical afterglow (AG) changing to a plateau phase and entering
the gradual transition to an asymptotic decline, which, in the CB model,
has roughly the form,
Fnu ~ [1/(t+t_b}^{\beta_O+1/2}] * nu^{-beta_O}
for a constant low-density SHB environment, or
Fnu ~ [1/ (t+t_b)^{beta_O+1}] * nu^{-beta_O}
for an isothermal sphere environment with a density propto 1/r^2.
t_b is the bending time of its canonical AG, and beta_O = Gamma - 1 ~ 1.1 is
the spectral index above the bend frequency. In the CB model, the initial
increase of the CB's radius, R^2 ~ t^2/(t^2+t_exp^2), where t_exp is the time
beyond which the CB's radius settles to its approximate constant value,
produces the initial rise of the synchrotron AG. The low density environments
of SHBs yields typically, t_b~ 10^5 s, and a long expansion time, t_exp, of the
CB's radius relative to its values in slow-rise optical AGs of long GRB such as
071010A (Covino et el. arXiv:0804.4367).