{
  "bibcode": "2017GCN.21806....1B",
  "body": "A. A. Breeveld (UCL-MSSL) and C. B. Markwardt (NASA/GSFC) report on\nbehalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 170903A\n3484 s after the BAT trigger (Markwardt et al., GCN Circ. 21793).\nNo optical afterglow consistent with the XRT position (Goad et al. GCN\nCirc. 21797) is 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 finding\nchart (FC) exposure and subsequent exposures are:\n\nFilter         T_start(s)   T_stop(s)      Exp(s)         Mag\n\nwhite_FC          3484         3634          147         >20.7\nwhite             3484         4865          344         >21.6\nv                 3640         5275          393         >19.7\nb                 4460         4660          197         >20.5\nu                 4255         4455          197         >21.0\nw1                4050         9664          362         >20.7\nm2                3845         5482          393         >20.4\nw2                4871         5071          197         >21.8\n\nThe magnitudes in the table are not corrected for the Galactic\nextinction due to the reddening of E(B-V) = 0.02 in the direction of the\nburst (Schlegel et al. 1998).",
  "circularId": 21806,
  "createdOn": 1504522928000,
  "email": "a.breeveld@ucl.ac.uk",
  "subject": "GRB 170903A: Swift/UVOT Upper Limits",
  "submitter": "Alice Breeveld at MSSL-UCL  <a.breeveld@ucl.ac.uk>",
  "eventId": "GRB 170903A"
}