{
  "bibcode": "2017GCN.21049....1K",
  "body": "N. P. M. Kuin (UCL-MSSL) and A. P. Beardmore (U. Leicester) report\non behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 170428A\n740 s after the BAT trigger (Beardmore et al., GCN Circ. 21042).\nNo optical afterglow consistent with the XRT position (Beardmore\net al., GCN Circ. 21047) 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 initial exposures\nare:\n\nFilter         T_start(s)   T_stop(s)      Exp(s)         Mag\n\nv                  740        16576         1101         >20.0\nb                  838        10823         1101         >21.0\nu                  813         5412          299         >19.5\nw1                 789         5207          216         >19.5\nm2                 764        17481         1102         >20.1\nw2                4392        11731         1082         >20.0\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.06 in the direction of the burst\n(Schlegel et al. 1998).",
  "circularId": 21049,
  "createdOn": 1493426435000,
  "email": "npkuin@gmail.com",
  "subject": "GRB 170428A: Swift/UVOT Upper Limits",
  "submitter": "Paul Kuin at MSSL  <npkuin@gmail.com>",
  "eventId": "GRB 170428A"
}