{
  "bibcode": "1999GCN...454....1J",
  "body": "GRB 991208 Optical Decay\n\nB. L. Jensen, J. Hjorth, H. Pedersen (University of Copenhagen),\nH. E. Kristen (CfA), L. Tomassi (Universita di Milano), \nE. Pian (ITESRE, Bologna) and K. Hurley (UCB SSL) report on behalf of a\nlarger European collaboration:\n\n\n\"We have imaged a significant fraction of the errorbox of GRB 991208\n(Hurley & Cline GCN #450) with the 2.5-m Nordic Optical Telescope. Three\n5-min R-band exposures were obtained with ALFOSC on 10.27 December 1999\nUT and three 3-min R-band exposures were obtained with StanCam on 11.85\nDecember 1999 UT. On both occasions the data were obtained during\ntwilight, at high (3 - 4) airmass and in bad seeing (2.5\" - 3\" FWHM). At\nthe location of the new radio (Frail GCN #451) and optical\n(Castro-Tirado et al. GCN #452) source we detect a transient optical\nsource [at RA(J2000) = 16:33:53.52, Dec = +46:27:21.0  (+- 0.4\")], thus\nconfirming its proposed identification with the afterglow of GRB 991208.\n We have performed PSF photometry on the images using DAOPHOT II/ALLSTAR\nand tied our photometric zeropoint to the USNO-A2.0 star 1350-08916561\nwhich has R = 15.8. On this system we find that the magnitudes of the\noptical transient were R = 18.7 +- 0.1 on 10.27 Dec and 20.0 +- 0.2 on\n11.85 Dec. We caution however that the latter data point may be affected\nby systematic uncertainties due to the difficult observing conditions.\nIf the optical transient follows a power law decay, the decay index is\n-2.15 and the predicted magnitude on 12.25 Dec is R = 20.2 +- 0.3. If we\ndiscard the 11.85 Dec data point and use R = 19.1 +- 0.1 on 11.25 Dec\n(GCN #452), the decay index is -0.98 and the predicted magnitude on\n12.25 Dec is R = 19.4 +- 0.2.\nThe NOT images will be posted at\nhttp://www.astro.ku.dk/~brian_j/grb991208/ .\"",
  "circularId": 454,
  "createdOn": 944972373000,
  "email": "brian_j@astro.ku.dk",
  "subject": "GRB 991208 Optical Decay",
  "submitter": "Brian Lindgren Jensen at U.of Copenhagen  <brian_j@astro.ku.dk>",
  "eventId": "GRB 991208"
}