{
  "submitter": "Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>",
  "submittedHow": "web",
  "format": "text/plain",
  "createdOn": 1750252174696,
  "body": "M. H. Siegel (PSU) and K. L. Page (U. Leicester)\nreport on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 250617B 797 s after the BAT trigger (Page et al., GCN Circ. 40760). A source consistent with the XRT position (Osborne et al., GCN Circ\n40767) is detected in the initial UVOT exposures. The lack of detection in the uvw2 and uvm2 filters would be consistent with the redshift reported by Corcoran et al. (GCN Circ. 40776).\n\nThe preliminary UVOT position is:\n    RA  (J2000) =  22:11:35.25 = 332.89686 (deg.)\n    Dec (J2000) = +32:43:57.1  =  32.73253 (deg.)\nwith an estimated uncertainty of 0.44 arc sec. (radius, 90% confidence).\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              797          946          147         18.18 +/- 0.05\nv                 1130         2528          172         18.72 +/- 0.19\nb                 1229         1596           58         18.91 +/- 0.18\nu                 1204         1397           39         18.10 +/- 0.19\nw1                1179         2408          156         19.32 +/- 0.28\nm2                1155         2384          117        >18.3\nw2                1106         2507          175        >19.2\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.087 in the direction of the burst\n(Schlegel et al. 1998).",
  "bibcode": "2025GCN.40778....1S",
  "circularId": 40778,
  "eventId": "GRB 250617B",
  "subject": "GRB 250617B: Swift/UVOT Detection"
}