{
  "subject": "GRB 180721A: Swift/UVOT Upper Limits",
  "eventId": "GRB 180721A",
  "bibcode": "2018GCN.23014....1K",
  "createdOn": 1532277775000,
  "circularId": 23014,
  "submitter": "Paul Kuin at MSSL  <npkuin@gmail.com>",
  "email": "npkuin@gmail.com",
  "body": "N. P. M. Kuin (UCL-MSSL) and B. Sbarufatti (PSU)\nreport on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 180721A\n120 s after the BAT trigger (Sbarufatti et al., GCN Circ. 22994).\nNo optical afterglow consistent with the XRT position (Goad et al, GCN\nCirc. 22997) is 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\nu_FC               120          370          246         >20.1\nv                  425         1693          156         >19.1\nb                  375         1642          175         >19.9\nu                  120         1617          529         >20.1\nw1                 474         1742          156         >19.6\nm2                1697         1717           19         >18.3\nw2                 401         1668          156         >20.5\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.07 in the direction of the burst\n(Schlegel et al. 1998)."
}