{
  "createdOn": 1767102304555,
  "submittedHow": "email",
  "bibcode": "2025GCN.43271....1B",
  "circularId": 43271,
  "subject": "GRB 251230A: Swift/UVOT detection",
  "submitter": "Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>",
  "eventId": "GRB 251230A",
  "body": "A.A. Breeveld (UCL-MSSL), N.P.M. Kuin (UCL-MSSL), S. Lanava (PSU) and M. De Pasquale (U. Messina) report on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 251230A 76s after the BAT trigger (Lanava et al., GCN Circ. 43252).\nA bright, fading source consistent with the enhanced XRT position (Osborne et al., GCN Circ. 43263) and optical detections (Lanava et al., GCN 43252; Li et al., GCN 43255; Busmann et al., GCN 43258; Masi et al., GCN 43260; Ghosh et al., GCN 43262; Ma et al., GCN 43265, He et al., GCN 43269) is detected in the initial UVOT exposures in the white, v, b, u and uvw1 filters.\n\nThe burst is also detected in the UV grism and, while there is some contamination from other zeroth orders, we obtain a tentative redshift of z=1.73.\n\nThe preliminary UVOT position is:\n    RA  (J2000) =  11:59:35.41 = 179.89756 (deg.)\n    Dec (J2000) = +11:26:19.2  =  11.43867 (deg.)\nwith an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).\n\nPreliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the finding chart (FC) and other early settled exposures are:\n\nFilter         T_start(s)   T_stop(s)      Exp(s)           Mag\n\nwhite_FC            76          226          147         13.61 ± 0.03\nwhite              868         1017          286         15.63 ± 0.02\nv                  619          638           19         14.69 ± 0.07\nb                  545          564           20         14.78 ± 0.05\nu_FC               288          538          246         13.77 ± 0.02\nuvw1               668          687           19         15.2  ± 0.1\nuvm2               643         1775          136         >18.8\nuvw2               594          614           19         >17.7\n\nThe magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.024 in the direction of the burst (Schlegel et al. 1998)."
}