{
  "bibcode": "2017GCN.20823....1E",
  "body": "S.W.K. Emery (UCL-MSSL) and C. B. Markwardt (NASA/GSFC)\nreport on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 170306A\n140 s after the BAT trigger (Markwardt et al., GCN Circ. 20819).\nNo optical afterglow consistent with the XRT position\n(Markwardt et al., GCN Circ. 20819)\nand the optical positions\n(Guidorzi et al., GCN Circ. 20820; Schady et al., GCN Circ. 20822)\nis detected in the initial UVOT exposures.\nPreliminary 3-sigma upper limits using the UVOT photometric system\n(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first\nfinding chart (FC) exposure and subsequent exposures are:\n\nFilter         T_start(s)   T_stop(s)      Exp(s)         Mag\n\nwhite_FC           140          290          147         >20.0\nu_FC               299          548          246         >18.9\nwhite              140          771          186         >20.4\nv                  629          821           39         >18.1\nb                  554          747           39         >18.6\nu                  299          722          265         >19.0\nw1                 678          870           39         >18.1\nm2                 653          846           39         >19.0\nw2                 604          796           39         >18.1\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.41 in the direction of the burst\n(Schlegel et al. 1998).",
  "circularId": 20823,
  "createdOn": 1488826322000,
  "email": "samuel.emery.15@ucl.ac.uk",
  "subject": "GRB 170306A: Swift/UVOT Upper Limits",
  "submitter": "Sam Emery at MSSL-UCL  <samuel.emery.15@ucl.ac.uk>",
  "eventId": "GRB 170306A"
}