{
  "subject": "GRB 240418A: Swift/UVOT Upper Limits",
  "eventId": "GRB 240418A",
  "submittedHow": "web",
  "bibcode": "2024GCN.36184....1S",
  "createdOn": 1713542779079,
  "submitter": "Sam Shilling at Lancaster University <shilling.sam@gmail.com>",
  "circularId": 36184,
  "body": "S. P. R. Shilling (Lancaster U.), S. R. Oates (Lancaster U.),  A. A. Breeveld (UCL-MSSL),  N. P. M. Kuin (UCL-MSSL) and M. H. Siegel (PSU)\nreport on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 240418A\n126 s after the BAT trigger (Siegel et al., GCN Circ. 36162).\nNo optical afterglow consistent with the XRT position (Evans et al., GCN Circ. 36166)\nis detected in the initial UVOT exposures.\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           126          276          147         >20.6\nu_FC               284          533          246         >19.4\nwhite              126         5282          347         >21.1\nv                 4072         4272          197         >19.3\nb                  539         5093          216         >20.2\nu                  284         4888          442         >19.9\nw1                4482         4682          197         >19.7\nm2                4276         4476          197         >19.5\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.057 in the direction of the burst\n(Schlegel et al. 1998)."
}