{
  "bibcode": "2018GCN.23360....1G",
  "body": "J. D. Gropp (PSU), M. De Pasquale\n(U. Instanbul) and Moss (George Washington University)\nreport on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 181020A\n122 s after the BAT trigger (Moss et al., GCN Circ. 23349).\nA fading source consistent with the XRT enhanced position\n(Goad et al. GCN Circ. 23351)\nis detected in the initial UVOT exposures.\n\nThe preliminary UVOT position is:\n    RA  (J2000) =  00:55:55.77 =  13.98239 (deg.)\n    Dec (J2000) = -47:22:51.9  = -47.38108 (deg.)\nwith an estimated uncertainty of 0.45 arc sec. (radius, 90% confidence).\nThis optical afterglow is also reported by VLT/X-shooter, Fynbo et al., GCN\nCirc. 23356;\nLCO Cerro Tololo, Cucchiara et al., GCN Circ. 23358;  and its position is\nconsistent\nwith the Fermi LAT Measurement reported in, Axelsson et al., GCN Circ.\n23350;\n\nPreliminary detections and 3-sigma upper limits using the UVOT photometric\nsystem\n(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures\nare:\n\nFilter         T_start(s)   T_stop(s)      Exp(s)           Mag\n\nb                     352             1027             97\n17.18+-0.07\nm2                  427               745             58      >18.06\nu_fc                 96               6797           768\n18.52+-0.09\nu                      96                346            245\n17.60+-0.08\nv                      21                 720              67\n 14.89+-0.04\nw1                  452                 769              58       >18.20\nw2                  379                1053             97       >18.56\n\nThe magnitudes in the table are not corrected for the Galactic extinction\ndue to the reddening of E(B-V) = 0.01 in the direction of the burst\n(Schlegel et al. 1998).\n\nWe note that the non-detection in the UV filters is expected for a source\nat the reported\nredshift z=2.94 (VLT/X-shooter, Fynbo et al., GCN Circ. 23356;), given\nthe Lyman forest absorption by intergalactic hydrogen.",
  "circularId": 23360,
  "createdOn": 1540147151000,
  "email": "jdg44@psu.edu",
  "subject": "GRB 181020A: Swift/UVOT Detection",
  "submitter": "Jeffrey Gropp at PSU  <jdg44@psu.edu>",
  "eventId": "GRB 181020A"
}