{
  "bibcode": "2021GCN.30746....1L",
  "body": "S. Laha (GSFC/UMBC/CRESST), E. Ambrosi (INAF-IASFPA),\nV. D'Elia (SSDC & INAF-OAR), P. A. Evans (U Leicester),\nC. Gronwall (PSU), J. A. Kennea (PSU),\nN. J. Klingler (GSFC/UMBC/CRESSTII), F. E. Marshall (NASA/GSFC),\nK. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU) and\nA. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 15:04:36 UT, the Swift Burst Alert Telescope (BAT) triggered and\nlocated GRB 210901A (trigger=1071488).  Swift slewed immediately to the burst. \nThe BAT on-board calculated location is \nRA, Dec 295.292, -76.932 which is \n   RA(J2000) = 19h 41m 10s\n   Dec(J2000) = -76d 55' 55\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The BAT light curve showed a complex structure\nwith a duration of about 60 sec. As this is an image trigger a more \ncomplete description of the lightcurve will require the ground pass data. \nThe peak count rate was ~500 counts/sec (15-350 keV), at ~0 sec after \nthe trigger. \n\nThe XRT began observing the field at 15:07:07.7 UT, 151.4 seconds after\nthe BAT trigger. Using promptly downlinked data we find a bright,\nfading, uncatalogued X-ray source with an enhanced position: RA, Dec\n295.2774, -76.9263 which is equivalent to:\n   RA(J2000)  = 19h 41m 06.57s\n   Dec(J2000) = -76d 55' 34.8\"\nwith an uncertainty of 1.9 arcseconds (radius, 90% containment). This\nlocation is 23 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 1.02\nx 10^21 cm^-2 (Willingale et al. 2013). \n\nThe initial flux in the 2.5 s image was 1.86e-09 erg cm^-2 s^-1 (0.2-10\nkeV). \n\nUVOT took a finding chart exposure of 150 seconds with the White filter\nstarting 157 seconds after the BAT trigger. No credible afterglow candidate has\nbeen found in the initial data products. The 2.7'x2.7' sub-image covers 100% of\nthe XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. \nThe 8'x8' region for the list of sources generated on-board covers 100% of the\nXRT error circle. The list of sources is typically complete to about 18 mag. No\ncorrection has been made for the expected extinction corresponding to E(B-V) of\n0.200. \n\nBurst Advocate for this burst is S. Laha (sib.laha AT gmail.com). \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": 30746,
  "createdOn": 1630509729000,
  "email": "klp5@leicester.ac.uk",
  "subject": "GRB 210901A: Swift detection of a burst",
  "submitter": "Kim Page at U.of Leicester  <klp5@leicester.ac.uk>",
  "eventId": "GRB 210901A"
}