TITLE: GCN CIRCULAR NUMBER: 36291 SUBJECT: GRB 240421B: Swift-BAT refined analysis DATE: 24/04/24 21:46:59 GMT FROM: Sibasish Laha at GSFC sibasish.laha@nasa.gov
S. D. Barthelmy (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-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 240421B (trigger #1223470) (Williams, et al., GCN Circ. 36208). The BAT ground-calculated position is RA, Dec = 299.685, -14.878 deg which is RA(J2000) = 19h 58m 48.03s Dec(J2000) = -14d 51' 36.4" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 4%.
The BAT light curve shows a complex structure with a duration of ~ 40 sec. T90 (15-350 keV) is 24.00 +- 9.22 sec (estimated error including systematics).
The time-averaged spectrum from T-30.4 to T+7.6 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.63 +- 0.52, and Epeak of 81.3 +- 22.3 keV (chi squared 50.17 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 6.4 +- 0.5 x 10^-06 erg/cm2 and the 1-sec peak flux measured from T-0.36 sec in the 15-150 keV band is 14.1 +- 1.6 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.55 +- 0.10 (chi squared 61.45 for 57 d.o.f.). 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/1223470
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