{
  "bibcode": "2008GCN..7567....1R",
  "body": "J.L. Racusin (PSU), S.R. Oates (UCL-MSSL), P. Schady (UCL-MSSL), S. T.\nHolland (CRESST/USRA/GSFC), D.N. Burrows (PSU), report on behalf of the\nSwift XRT and UVOT teams:\n\nWe have analyzed the first 19 days of Swift XRT data from GRB 080319B\n(Racusin et al. GCN 7427), with a total exposure time of 200 ks.  The\nlight curve can be fit by a triple broken power-law with initial decay\nslope of 1.54+/-0.01, breaking at 2790+/-664 s to a slope of 1.85+/-0.05,\nbreaking again at 41.4+/-9.0 ks to a slope of 1.17+/-0.06, and finally\nbreaking at 1.04+/-0.43 Ms to a slope of 2.9+/-2.3.\n\nIf this last break is interpreted as a jet break, the jet opening\nhalf-angle is 8 degrees x (n/10 cm^-3)^(1/8).  We obtained Eiso=1.3x10^54\nergs (25 kev - 7 MeV) from Golenetskii et al. (GCN 7482), assuming\ncosmological parameters of H_0=70 km/s/Mpc, Omega_M=0.3, Omega_Lambda =\n0.7.  The corresponding beaming corrected energy is 1.3 x 10^52 ergs.\n\nThe uncertanties in the post-jet break slope and time are large.\nTherefore, the evidence for a break is preliminary and further\nobservations will be required to confirm it.\n\nLate-time UVOT white filter observations are also suggestive of a break at\napproximately the same time as the X-ray break.  However, further\nobservations are needed to confirm the break because the afterglow flux is\nnear the UVOT detection limit.\n\nWe strongly encourage additional late-time optical follow-up to further\ntest for achromaticity and constrain the possible jet break.\n\nThis circular is an official product of the Swift Team.",
  "circularId": 7567,
  "createdOn": 1207597491000,
  "email": "racusin@astro.psu.edu",
  "subject": "GRB 080319B: Potential Jet Break Observed by Swift-XRT and UVOT",
  "submitter": "Judith Racusin at PSU  <racusin@astro.psu.edu>",
  "eventId": "GRB 080319B"
}