TITLE: GCN CIRCULAR NUMBER: 43234 SUBJECT: GRB 251221A: Swift-BAT refined analysis DATE: 25/12/25 05:09:07 GMT FROM: Mike Moss at NASA GSFC <mikejmoss3@gmail.com> A. Y. Lien (U Tampa), E. Ambrosi (INAF-IASFPA), S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU) (i.e. the Swift-BAT team): Using the data set from T-240 to T+962 sec from the recent telemetry downlink, we report further analysis of BAT GRB 251221A (trigger #1426088) (Ambrosi, et al., GCN Circ. 43166). The BAT ground-calculated position is RA, Dec = 101.422, 0.738 deg which is RA(J2000) = 06h 45m 41.4s Dec(J2000) = +00d 44' 15.8" with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 42%. The mask-weighted light curves displays a complicated multi-pulsed light curve. The T90 (15-350 keV) is 56.86 +- 7.05 sec (estimated error including systematics). The time-averaged spectrum from T-38.10 to T+27.74 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.25 +- 0.13. The fluence in the 15-150 keV band is 2.0 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+2.91 sec in the 15-150 keV band is 1.1 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1426088 View this GCN Circular online at https://gcn.nasa.gov/circulars/43234. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...