{
  "bibcode": "2019GCN.26526....1K",
  "body": "N. P. M. Kuin (UCL-MSSL) and S. L. Laha (GSFC/UMBC/CRESST)\nreport on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 191220A\n138 s after the BAT trigger (Laha et al., GCN Circ. 26516).  No optical\nafterglow consistent with the XRT position (Laha et al. GCN Circ. 26516)\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\nu_FC               138          387          246         >19.8\nu                  138         6726         1061         >20.0\nw1                 446         6521          687         >19.6\nm2                 420         6316          687         >19.9\nw2                 396         6766          719         >21.1\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.14 in the direction of the burst\n(Schlegel et al. 1998).",
  "circularId": 26526,
  "createdOn": 1576896324000,
  "email": "npkuin@gmail.com",
  "subject": "GRB 191220A: Swift/UVOT Upper Limits",
  "submitter": "Paul Kuin at MSSL  <npkuin@gmail.com>",
  "eventId": "GRB 191220A"
}