{
  "bibcode": "2018GCN.22570....1K",
  "body": "N. P. M. Kuin (UCL-MSSL) and C. B. Markwardt (GSFC) report\non behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB\n180331A 116 s after the BAT trigger (Markwardt et al., GCN Circ.\n22568).  No optical afterglow consistent with the XRT position\n(Evans et al. GCN Circ. 22569) is detected in the initial UVOT\nexposures.\nPreliminary 3-sigma upper limits using the UVOT photometric\nsystem (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the\nfirst finding chart (FC) exposure and subsequent exposures are:\n\nFilter         T_start(s)   T_stop(s)      Exp(s)         Mag\n\nwhite_FC           116          266          147         >20.2\nu_FC               274          524          246         >19.9\nwhite              116         1373          371         >20.4\nv                  604         1250           78         >18.6\nb                  530         1350           78         >19.4\nu                  274          524          246         >19.9\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.60 in the direction of the burst\n(Schlegel et al. 1998).",
  "circularId": 22570,
  "createdOn": 1522495581000,
  "email": "npkuin@gmail.com",
  "subject": "GRB 180331A: Swift/UVOT Upper Limits",
  "submitter": "Paul Kuin at MSSL  <npkuin@gmail.com>",
  "eventId": "GRB 180331A"
}