{
  "bibcode": "2021GCN.30296....1B",
  "body": "M. G. Bernardini (INAF-OAB), J.D. Gropp (PSU), J. A. Kennea (PSU),\nN. J. Klingler (PSU), N. P. M. Kuin (UCL-MSSL),\nS. Laha (GSFC/UMBC/CRESST), A. Y. Lien (GSFC/UMBC),\nA. Melandri (INAF-OAB), K. L. Page (U Leicester), D. M. Palmer (LANL),\nT. Sbarrato (INAF-OAB), B. Sbarufatti (PSU), M. H. Siegel (PSU) and\nA. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift\nObservatory Team:\n\nAt 17:04:36 on 2021-06-21 UT, the Swift Burst Alert Telescope (BAT) triggered\non a burst from the Soft Gamma Repeater Swift J1555.2-5402 \n(trigger=1057131).  Swift was already observing the source at that time. \nThe BAT on-board calculated location is \nRA, Dec 238.812, -54.063 which is \n   RA(J2000) = 15h 55m 15s\n   Dec(J2000) = -54d 03' 45\"\nwith an uncertainty of 3 arcmin (radius, 90% containment, including \nsystematic uncertainty).  The immediately available BAT light curve\nshowed a single high bin on the 64 ms timescale, consistent with\nthe on-board trigger duration of 8 milliseconds for a single short spike. \nThe peak count rate was ~1000 counts/sec (15-350 keV) on the 64 ms\ntimescale, at ~0 sec after the trigger. \n\nUsing promptly downlinked data we find an X-ray source with an\nenhanced position: RA, Dec 238.7871, -54.0615 which is equivalent to:\n   RA(J2000)  = 15h 55m 08.90s\n   Dec(J2000) = -54d 03' 41.4\"\nwith an uncertainty of 2.0 arcseconds (radius, 90% containment), which is\nconsistent with the position of Swift J1555.2-5402. This\nposition may be improved as more data are received; the latest position\nis available at https://www.swift.ac.uk/sper. \n\nA power-law fit to a spectrum formed from promptly downlinked event\ndata does not constrain the column density. \n\nUVOT took a finding chart exposures of 150 seconds with the white\nfilter and 250 seconds with the U filter.  No credible afterglow\ncandidate has been  found in the initial data products. The 2.7'x2.7'\nsub-image covers 100% of the  XRT error circle. Because of the density\nof catalogued stars, further analysis  is required to report an upper\nlimit for any afterglow in the sub-image. The  8'x8' region for the\nlist of sources generated on-board covers 100% of the XRT  error\ncircle. The list of sources is typically complete to about 18.0 mag. \nNo  correction has been made for the large, but uncertain, extinction\nexpected. \n\nThis source lies within the current (Sector 39) field-of-view of TESS camera 2. \n\nThe current list of bursts from this source detected by BAT\nnow stands at:\n\n2021-06-03 09:45:46 GCN #30120 (discovery)\n2021-06-05 23:52:04 ATEL #14690\n2021-06-07 12:33:40 ATEL #14690\n2021-06-13 06:35:22  not previously reported\n2021-06-16 14:44:30  not previously reported\n2021-06-21 17:04:36 This GCN",
  "circularId": 30296,
  "createdOn": 1624296539000,
  "email": "palmer@lanl.gov",
  "subject": "Swift Trigger 1057131: detection of a burst from SGR Swift J1555.2-5402",
  "submitter": "David Palmer at LANL  <palmer@lanl.gov>"
}