{
  "bibcode": "2021GCN.29862....1B",
  "body": "A. A. Breeveld (UCL-MSSL) and M. J. Moss (GWU) report on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 210420B 147s after the BAT trigger \n(Moss et al., GCN Circ. 29844 and updated in Lien et al., GCN Circ. 29854).\nA fading source consistent with the optical counterpart reported by Lipunov et al. GCN Circ. 29845, \nOksanen GCN Circ. 29846, Hu et al. GCN Circ. 29847, Tianrui et al. GCN Circ. 29848, Leonini et al. \nGCN Circ. 29851, de Ugarte Postigo et al. GCN Circ. 29852 and Watson et al. GCN Circ. 29858, is \ndetected in the initial UVOT exposures.\n\nPreliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. \n1358, 373) for the first finding chart (_fc) exposure and other early exposures are:\n\nFilter         T_start(s)   T_stop(s)      Exp(s)           Mag\n\nu_fc               147          391          240         16.2 �� 0.04\nu                18793        19317          512         18.6 �� 0.1\nv                  447          467           20         16.7 �� 0.2\nb                  397          417           19         17.1 �� 0.1\nw1                 496          516           20         16.5 �� 0.2\nm2                 620         1121           39         17.2 �� 0.2\nw2                1201         1371           39         17.6 �� 0.2\n\nThe magnitudes in the table are not corrected for the Galactic extinction due to the reddening of \nE(B-V) = 0.022 in the direction of the burst (Schlegel et al. 1998).",
  "circularId": 29862,
  "createdOn": 1619016138000,
  "email": "a.breeveld@ucl.ac.uk",
  "subject": "GRB 210420B: Swift/UVOT Detection",
  "submitter": "Alice Breeveld at MSSL-UCL  <a.breeveld@ucl.ac.uk>",
  "eventId": "GRB 210420B"
}