{
  "bibcode": "2008GCN..7682....1D",
  "body": "Many long GRBs have optical light-curves which are initially slowly \nrising. The optical light curve of the short hard burst (SHB) 080503 (Mao \net al. GCN 7665; Ukwatta et al. GCN 7673; Guidorzi et al. GCN 7674) \ndiscovered by Perley et al. (GCNs 7678, 7680) may be their analog \nslow-rise optical afterglow (AG) changing to a plateau phase and entering \nthe gradual transition to an asymptotic decline, which, in the CB model, \nhas roughly the form,\n\n            Fnu ~ [1/(t+t_b}^{\\beta_O+1/2}] * nu^{-beta_O}\n\nfor a constant low-density SHB environment, or\n\n            Fnu  ~ [1/ (t+t_b)^{beta_O+1}] * nu^{-beta_O}\n\nfor an isothermal sphere environment with a density propto 1/r^2.\nt_b is the bending time of its canonical AG, and beta_O = Gamma - 1 ~ 1.1 is \nthe spectral index above the bend frequency. In the CB model, the initial \nincrease of the CB's radius, R^2 ~ t^2/(t^2+t_exp^2), where t_exp is the time \nbeyond which the CB's radius settles to its approximate constant value, \nproduces the initial rise of the synchrotron AG.  The low density environments \nof SHBs yields typically, t_b~ 10^5 s, and a long expansion time, t_exp, of the \nCB's radius relative to its values in slow-rise optical AGs of long GRB such as \n071010A (Covino et el. arXiv:0804.4367).",
  "circularId": 7682,
  "createdOn": 1210045815000,
  "email": "arnon@physics.technion.ac.il",
  "subject": "GRB 080503: Slow-rise optical AG ?",
  "submitter": "Arnon Dar at Technion-Israel Inst. of Tech  <arnon@physics.technion.ac.il>",
  "eventId": "GRB 080503"
}