TITLE: GCN CIRCULAR NUMBER: 41598 SUBJECT: GRB 250828B: Swift-BAT refined analysis DATE: 25/08/29 23:16:38 GMT FROM: Amy yarleen@gmail.com

M. J. Moss (GSFC), S. D. Barthelmy (GSFC), R. Gupta (GSFC), P. A. Evans (U Leicester), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (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-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 250828B (trigger #1345836) (Evans et al., GCN Circ. 41581). The BAT ground-calculated position is RA, Dec = 124.867, -17.352 deg which is RA(J2000) = 08h 19m 28.2s Dec(J2000) = -17d 21' 07.8" with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 64%.

The mask-weighted light curve shows a complex structure. The main pulse starts and peaks at ~T0, and ends at ~T+5 s. In addition, there are some weak emission that starts prior to the main pulse at ~T-60 s and persists after the main pulse until ~T+60 s. T90 (15-350 keV) is 94.09 +- 32.03 sec (estimated error including systematics).

The time-averaged spectrum from T-56.23 to T+76.66 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.13 +- 0.19. The fluence in the 15-150 keV band is 1.5 +- 0.2 x 10^-06 erg/cm2. The 1-sec peak photon flux measured from T+0.12 sec in the 15-150 keV band is 1.7 +- 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/1345836

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