{
  "bibcode": "2025GCN.41494....1L",
  "submittedHow": "web",
  "submitter": "Rahul Gupta at NASA GSFC <rahul.gupta@nasa.gov>",
  "circularId": 41494,
  "format": "text/plain",
  "createdOn": 1755873090284,
  "eventId": "GRB 250821A",
  "subject": "GRB 250821A: Swift-BAT refined analysis",
  "body": "A. Y. Lien (U Tampa), S. D. Barthelmy (GSFC),\nS. Dichiara (PSU), R. Gupta (GSFC),\nH. A. Krimm (NSF), S. Laha (GSFC/UMBC),\nC. B. Markwardt (GSFC), M. J. Moss (GSFC),\nD. M. Palmer (LANL), T. Parsotan (GSFC),\nD. Sadaula (GSFC/UMBC), T. Sakamoto (AGU)\n(i.e. the Swift-BAT team):\n\nUsing the data set from T-240 to T+963 sec from the recent telemetry downlink,\nwe report further analysis of BAT GRB 250821A (trigger #1344131)\n(Dichiara, et al., GCN Circ. 41462).  The BAT ground-calculated position is\nRA, Dec = 358.427, -28.631 deg which is\n   RA(J2000)  =  23h 53m 42.6s\n   Dec(J2000) = -28d 37' 53.3\"\nwith an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).\nThe partial coding was 64%.\n\nThe mask-weighted BAT light curve exhibits a short-duration main emission\nstarting from ~T-0.5 to ~T+1.2 sec, followed by a weaker, extended emission\nwhich last up to ~ T+18 sec.\nT90 (15-350 keV) is 1.52 +- 0.37 sec (estimated error including systematics).\n\nThe time-averaged spectrum from T-0.46 to T+1.20 sec is best fit by a simple\npower-law model.  The power law index of the time-averaged spectrum is\n0.83 +- 0.41.  The fluence in the 15-150 keV band is 1.3 +- 0.3 x 10^-07 erg/cm2.\nThe 1-sec peak photon flux measured from T+0.06 sec in the 15-150 keV band\nis 0.9 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence\nlevel.\n \nThe results of the batgrbproduct analysis are available at\nhttps://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1344131"
}