{
  "bibcode": "2020GCN.28342....1B",
  "body": "A. A. Breeveld (UCL-MSSL) and K. K. Simpson (PSU)\nreport on behalf of the Swift/UVOT team:\n\nThe Swift/UVOT began settled observations of the field of GRB 200901A 3053 s after the BAT trigger \n(Simpson et al., GCN Circ. 28335).\nA possible optical afterglow consistent with the XRT position (Kennea et al., GCN Circ. 28341) is \ndetected in the initial UVOT exposures in the white filter only. It is not clear whether the source \nis fading.\nPreliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. \n2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are:\n\nFilter         T_start(s)   T_stop(s)      Exp(s)         Mag\n\nwhite_FC          3053         3202          147         20.6 +/- 0.3\nwhite             3916         4115          197         20.5 +/- 0.2\nv                 4326         4526          197         >19.1\nb                 3711         3910          197         >20.4\nu                 3211         4987          290         >20.0\nw1                4736         4936          197         >19.1\nm2                4531         4731          197         >19.1\nw2                4121         4321          197         >19.3\n\nThe magnitudes in the table are not corrected for the Galactic extinction due to the reddening of \nE(B-V) = 0.02 in the direction of the burst (Schlegel et al. 1998).",
  "circularId": 28342,
  "createdOn": 1598991367000,
  "email": "a.breeveld@ucl.ac.uk",
  "subject": "GRB 200901A: Swift/UVOT Detection",
  "submitter": "Alice Breeveld at MSSL-UCL  <a.breeveld@ucl.ac.uk>",
  "eventId": "GRB 200901A"
}