{
  "body": "S. R. Oates (Lancaster U.) and T. M. Parsotan (GSFC)\nreport on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 250603A\n105 s after the BAT trigger (Parsotan et al., GCN Circ. 40613).\nNo optical afterglow consistent with the enhanced XRT position\n(Beardmore et al., GCN Circ. 40616) is detected in the initial UVOT exposures.\n\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           105          255          147         >20.4\nu_FC               318          567          246         >19.7\nwhite              105         1531          382         >21.0\nv                  647         5129          190         >19.0\nb                  573         1516           97         >19.6\nu                  318         1491          324         >19.8\nw1                 697         1467           78         >18.7\nm2                 672         1442           97         >18.5\nw2                 623         5029          294         >19.2\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 1.89 in the direction of the burst\n(Schlegel et al. 1998).\n",
  "eventId": "GRB 250603A",
  "bibcode": "2025GCN.40619....1O",
  "submittedHow": "email",
  "circularId": 40619,
  "submitter": "Samantha Oates at University of Birmingham <samantha.oates@alumni.ucl.ac.uk>",
  "subject": "GRB 250603A: Swift/UVOT Upper Limits",
  "createdOn": 1748956492796
}