TITLE: GCN CIRCULAR NUMBER: 38701 SUBJECT: GRB 241228A: Swift-BAT refined analysis DATE: 24/12/29 03:23:00 GMT FROM: Amy yarleen@gmail.com

D. Sadaula (GSFC/UMBC), S. D. Barthelmy (GSFC), D’Elia (SSDC & INAF-OAR), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss (GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), T. Sakamoto (AGU) (i.e. the Swift-BAT team):

Using the data set from T-240 to T+1101 sec from the recent telemetry downlink, we report further analysis of BAT GRB 241228A (trigger #1277277) (D'Elia et al., GCN Circ. 38681). The BAT ground-calculated position is RA, Dec = 344.810, 18.608 deg which is RA(J2000) = 22h 59m 14.4s Dec(J2000) = +18d 36' 28.6" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 39%.

The mask-weighted light curve shows several overlapping pulses that start at ~T-5 s and end at ~T+5 s. T90 (15-350 keV) is 8.06 +- 0.53 sec (estimated error including systematics).

The time-averaged spectrum from T-5.16 to T+4.71 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.90 +- 0.24, and Epeak of 61.0 +- 5.2 keV (chi squared 82.23 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 3.0 +- 0.1 x 10^-06 erg/cm2 and the 1-sec peak flux measured from T+1.94 sec in the 15-150 keV band is 13.1 +- 0.6 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/1277277

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