{
  "bibcode": "2008GCN..7627....1K",
  "body": "D. A. Kann, S. Schulze (TLS Tautenburg) & A. C. Updike (Clemson \nUniversity) report:\n\nIn light of recent reports on the further evolution of GRB 080319B, we did \na preliminary analysis of the multiwavelength data set.\n\nJet Break:\nRacusin et al. (GCN 7567) reported the existence of a potential jet break \nat 1.04 +/- 0.43 Ms in the X-ray band, with a hint of a steeper decay seen \nin the optical as well. Using the most up-to-date data from  the Swift XRT \nlight curve repository (Evans et al. 2007), we confirm the  findings of \nthe Swift team and derive (using data starting at 0.5 days after the GRB):\n\nchi^2/d.o.f. = 39/58\nalpha_1 = 1.01 +/- 0.05\nalpha_2 = 2.40 +/- 0.39\nt_b = 9.43 +/- 1.73 days (0.815 +/- 0.149 Ms)\nn = 5 fixed, no \"host galaxy\"\n\nThese values are in agreement with those of the Swift team, with \nsignificantly reduced errors. We note that there seems to be a steep decay \nin the X-ray light curve from 0.35 to 0.5 days, and a similar evolution \nhas been reported in the optical (Krugly et al., GCN 7519) at about the \nsame time. This is reminiscent of the X-ray light curve of GRB 070110 \n(Troja et al. 2007).\n\nIn the optical, we add data from Perley et al. (GCN 7535) and Tanvir et \nal. (GCN 7621) to the data set from Bloom et al. 2008 (arXiv:0803.3215). \nTanvir et al. report a significant reddening, which we confirm. \n\nAt the moment, it is unclear how much the host galaxy and a potential \nsupernova contribute in the g band, but a roughly achromatic steepening is \nseen in this band (Tanvir et al.) in comparison to the X-ray light curve.\n\nEnergetics:\nUsing the prompt emission data derived from Konus-Wind (Golenetskii et \nal., GCN 7482), we find in the bolometric band (1 - 10000 keV, host \nframe):\n\nE_iso = 1.32 +/- 0.03 x 10^54 erg (log E_iso = 54.12)\n\nIn the sample of Kann et al. 2007 (arXiv:0712.2186), only two GRBs (000131 \nand 990123) exceed this value.\n\nUsing the jet break time derived above, as well as the redshift z=0.937 \n(Vreeswijk et al., GCN 7444), and assuming standard parameters \n(constant-density medium, circumburst density n = 10 cm^-3, efficiency eta \n= 0.2), we find:\n\ntheta_jet = 10.24 +/- 0.71 degrees\nE_jet = 2.11 +/- 0.30 x 10^52 erg (log E_jet = 52.3)\n\nThis value is comparable to or higher than for GRB 050904 (Tagliaferri et \nal. 2005, Frail et al. 2006), GRB 050820A (Cenko et al. 2006) and GRB \n070125 (Updike et al. 2008, Chandra et al. 2008), implying that this is \nthe fourth hyper-energetic GRB (cf. Chandra et al. 2008). We note that \nbroadband modeling may refine the circumburst density; if it is \nsignificantly higher than 10 cm^-3, the colimation-corrected energy \nwill also be significantly higher.\n\nSupernova:\nIn the i' band, the afterglow does not show a late steep decay, indicating \nthe possibility of a supernova that is by now contributing to the optical \ntransient (Tanvir et al.). Using the composite light curve (Bloom et al.) \nshifted to the i' band (using the early Rc - i' color), and assuming an \nachromatic break (t_b, alpha_2 fixed from the X-ray fit) and no host \ngalaxy, we find, using data after 0.7 days (after the steep decay + \nplateau phase, Krugly et al.):\n\nchi^2/d.o.f. = 44/10 (scatter)\nalpha_1 = 1.33 +/- 0.02\nk = 2.40 +/- 0.15\ns = 1 fixed (stretch factor)\n\nk is the peak luminosity in units of the SN 1998bw peak luminosity. This \nis a high value (Ferrero et al. 2006) and represents an upper limit on the \nSN flux. Assuming m_host(i') = 25, we find k = 1.24 +/- 0.14, a more \nreasonable result, indicating the contribution of a host galaxy to \nthe late afterglow.\n\nThis message may be cited.",
  "circularId": 7627,
  "createdOn": 1208372293000,
  "email": "kann@tls-tautenburg.de",
  "subject": "GRB 080319B: Jet Break, Energetics, Supernova",
  "submitter": "Alexander Kann at TLS Tautenburg  <kann@tls-tautenburg.de>",
  "eventId": "GRB 080319B"
}