{
  "bibcode": "2021GCN.29706....1S",
  "body": "M. H. Siegel (PSU) and E. Troja (NASA/GSFC/UMCP)\nreport on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 210318A\n127 s after the BAT trigger (Troja et al., GCN Circ. 29662).\nNo optical afterglow consistent with the XRT position\n(Troja et al. GCN Circ. 29662)\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           127          277          147         >20.5\nu_FC               285          535          246         >19.9\nwhite              127         1188          353         >21.0\nv                  614         1064           58         >18.6\nb                  541         1163           58         >19.3\nu                  285          535          246         >19.9\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.017 in the direction of the burst\n(Schlegel et al. 1998).",
  "circularId": 29706,
  "createdOn": 1616583942000,
  "email": "mhs18@psu.edu",
  "subject": "GRB 210318A: Swift/UVOT Upper Limits",
  "submitter": "Mike Siegel at PSU/Swift MOC  <mhs18@psu.edu>",
  "eventId": "GRB 210318A"
}