{
  "bibcode": "2007GCN..6564....1S",
  "body": "A. Stefanescu (1), Z. Ioannou (2)(4), G. Kanbach (1), S. Duscha (1), F. \nSchrey (1), A. Slowikowska (2)(3), H. Steinle (1)\n((1)=MPE Garching, (2)=FORTH, Heraklion (3)=NCAC, Torun, (4)=Univ. of \nCrete) of the OPTIMA-Burst Team report the following:\n\nOPTIMA-Burst at the 1.3m Skinakas Observatory, of the University of\nCrete, Greece observed the Swift XRT error circle of GRB 070621 (GCN\nCirc 6560, B. Sbarufatti et al.). Observations started at 23:54:52 UT \n(2233s after the trigger) at an airmass of 2.5.\n\nWe see no source at the XRT error circle, neither in single exposures, \nnor in stacked exposures. Data of the exposures are:\n\nt-t_0 (mid exp)  t_exp     R-limit\n2263s            60s       20.0         (first exposure)\n3271s            1680s     20.9         (stack of all avail. exposures)",
  "circularId": 6564,
  "createdOn": 1182480096000,
  "email": "astefan@mpe.mpg.de",
  "subject": "GRB070621: OPTIMA-Burst optical upper limit",
  "submitter": "Alexander Stefanescu at MPE  <astefan@mpe.mpg.de>",
  "eventId": "GRB 070621"
}