{
  "body": "M. H.Siegel (PSU) and A. Melandri (INAF-OAR) on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 250312A 464s after the BAT trigger (Melandri et al., GCN Circ. 39686). No optical afterglow consistent with the enhanced XRT position (Evans et al., GCN Circ. 39693) is detected in the initial UVOT exposures.Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are:\n\nFilter         T_start(s)   T_stop(s)      Exp(s)         Mag\n\nwhite (fc)         464         1563          165            >20.47\nwhite              743         1563          223            >20.50\nb                  718         1539           38            >18.84\nb                 6529        33943         1081            >20.52\nu                 6324        23538          403            >19.80\nuvw1             21814        22713          885            >19.99\nuvm2             10515        16904         1012            >19.85\nuvw2              6939        28312         1082            >20.24\n\nThe magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.015 in the direction of the burst (Schlegel et al. 1998).",
  "submitter": "Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>",
  "bibcode": "2025GCN.39765....1S",
  "eventId": "GRB 250312A",
  "submittedHow": "web",
  "format": "text/plain",
  "circularId": 39765,
  "subject": "GRB250312A: Swift/UVOT Upper Limits",
  "createdOn": 1742242861161
}