{
  "bibcode": "2025GCN.39409....1S",
  "format": "text/plain",
  "circularId": 39409,
  "eventId": "GRB 250221A",
  "subject": "GRB 250221A: Swift/UVOT Detection",
  "createdOn": 1740151659182,
  "submitter": "Sam Shilling at Lancaster University <shilling.sam@gmail.com>",
  "submittedHow": "web",
  "body": "S.P.R. Shilling (Lancaster U.), A.A. Breeveld (UCL-MSSL)\nand R. Caputo (NASA/GSFC) report on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 250221A\n107 s after the BAT trigger (Caputo et al., GCN Circ. 39396).\nA source consistent with the enhanced XRT position\n(Beardmore et al., GCN Circ. 39404) is detected in the initial UVOT exposures\nand appears to be fading. An optical candidate in this field is\nalso detected by Watson et al., (GCN Circ. 39397) and by\nMelandri et al., (GCN Circ. 39406).\n\nPreliminary detections and 3-sigma upper limits using the UVOT photometric system\n(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: \n\nFilter         T_start(s)   T_stop(s)      Exp(s)           Mag\n\nwhite              127          277\t      147\t    17.52 +/- 0.04\nwhite\t\t   620\t\t639\t       19\t    18.41 +/- 0.17\nv                  107          118\t       10\t    17.10 +/- 0.32\nv\t\t  4484\t       4683\t      197\t    >18.8\nb                  595          615            19\t    >18.7  \nu                  340          590           245\t    17.78 +/- 0.07           \nw1                4894         5041           144\t    >19.0  \nm2                4689\t       4889\t      197\t    >18.6                            \nw2                4279\t       4479\t      197\t    >18.7         \n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.332 in the direction of the burst\n(Schlegel et al. 1998)."
}