{
  "bibcode": "2020GCN.28696....1A",
  "body": "E. Ambrosi (INAF-IASFPA), A. D'Ai (INAF-IASFPA), V. D'Elia (SSDC),\nN. J. Klingler (PSU), H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC),\nK. L. Page (U Leicester), T. Sakamoto (AGU), B. Sbarufatti (PSU) and\nA. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 05:47:26 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 201020A (trigger=1000926).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 261.246, +31.425 which is \n   RA(J2000) = 17h 24m 59s\n   Dec(J2000) = +31d 25' 30\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a single-peaked\nstructure with a duration of about 20 sec.  The peak count rate\nwas ~1800 counts/sec (15-350 keV), at ~17 sec after the trigger. \n\nThe XRT began observing the field at 05:49:47.6 UT, 141.5 seconds after\nthe BAT trigger. Using promptly downlinked data we find a fading,\nuncatalogued X-ray source with an enhanced position: RA, Dec 261.2279,\n31.4288 which is equivalent to:\n   RA(J2000)  = 17h 24m 54.71s\n   Dec(J2000) = +31d 25' 43.8\"\nwith an uncertainty of 2.2 arcseconds (radius, 90% containment). This\nlocation is 57 arcseconds from the BAT onboard position, within the BAT\nerror circle. This position may be improved as more data are received;\nthe latest position is available at https://www.swift.ac.uk/sper. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata gives a column density consistent with the Galactic value of 3.70\nx 10^20 cm^-2 (Willingale et al. 2013). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 144 seconds after the BAT trigger. There is a candidate afterglow in\nthe rapidly available 2.7'x2.7' sub-image at\n  RA(J2000)  =\t17:24:54.67 = 261.22779\n  DEC(J2000) = +31:25:42.0  =  31.42834\nwith a 90%-confidence error radius of about 0.62 arc sec. This position is 5.4\narc sec. from the center of the XRT error circle. The estimated magnitude is\n18.14 with a 1-sigma error of about  0.15. No correction has been made for the\nexpected extinction corresponding to E(B-V) of 0.04. \n\nBurst Advocate for this burst is E. Ambrosi (elena.ambrosi AT inaf.it). \nPlease contact the BA by email if you require additional information\nregarding Swift followup of this burst. In extremely urgent cases, after\ntrying the Burst Advocate, you can contact the Swift PI by phone (see\nSwift TOO web site for information: http://www.swift.psu.edu/)",
  "circularId": 28696,
  "createdOn": 1603173593000,
  "email": "klp5@leicester.ac.uk",
  "subject": "GRB 201020A: Swift detection of a burst with an optical counterpart.",
  "submitter": "Kim Page at U.of Leicester  <klp5@leicester.ac.uk>",
  "eventId": "GRB 201020A"
}