{
  "bibcode": "2002GCN..1369....1M",
  "body": "D. Malesani, G. Ghisellini, S. Covino (Brera Observ., Milan) and\nD. Lazzati (IoA Cambridge, UK) report:\n\nAccording to the idea of Frail et al. (2001, ApJ, 562, L55) that the jet\n\nenergies of GRBs are universal, an achromatic jet break in the afterglow\n\nlightcurve is predicted for all bursts at the time\n\nt_jet = 20.4 (1+z) / (E_gamma/1e52) days,\n\nwhere E_gamma is the observed (i.e. isotropic) energy of the prompt\nemission. This result is independent of the unknown efficiency and\ncircumburst density.\n\nFor GRB020405, with z=0.69 (GCN 1330 and GCN 1340) and E_gamma>4.3e52\nerg (assuming H_0=65, Omega_m=0.3, Omega_Lambda=0.7 and taking the\nfluence to be larger than the reported value in the 25-100 keV band:\n3e-5 erg/cm2, GCN 1325), we have t_jet<8 days. Hence the break\nshould have occured before April 13.\n\nOur V-band data (GCN 1337, 1345) connect very well with a previous\nmeasurement by Palazzi et al. (GCN 1328), who use the same calibration\nstars. The decay slope is hence very well defined (1.52+-0.04), making\neasier the possible detection of the predicted break (see the lightcurve\n\nat:  http://www.merate.mi.astro.it/~gabriele/020405.html ).\nSince both the detection or the non-detection of the break would be very\n\nimportant to constrain Frail et al. idea, we urge photometric\nobservations of the afterglow of this burst.\n\nThis message can be cited.",
  "circularId": 1369,
  "createdOn": 1018713825000,
  "email": "malesani@merate.mi.astro.it",
  "subject": "GRB020405: predicted break",
  "submitter": "Daniele Malesani at Obs.Astro. di Brera  <malesani@merate.mi.astro.it>",
  "eventId": "GRB 020405"
}