TITLE: GCN CIRCULAR NUMBER: 37539 SUBJECT: GRB 240912A: Swift-BAT refined analysis DATE: 24/09/17 23:48:22 GMT FROM: Mike Moss at NASA GSFC mikejmoss3@gmail.com
T. Parsotan (GSFC), S. D. Barthelmy (GSFC), P. A. Evans (U Leicester), 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), 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 240912A (trigger #1253910) (P. A. Evans, et al., GCN Circ. 37466). The BAT ground-calculated position is RA, Dec = 124.625, 33.999 deg which is RA(J2000) = 08h 18m 29.9s Dec(J2000) = +33d 59' 56.2" with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 86%.
The light curve displays an interval of weak flat emission for ~45 seconds before a bright multi-pulsed emission period. There is a possible shallow rise of emission at ~T0+280 seconds coincident with the flare seen in the XRT afterglow. T90 (15-350 keV) is 113.24 +- 7.83 sec (estimated error including systematics).
The time-averaged spectrum from T-2.35 to T+373.02 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 1.43 +- 0.11, and Epeak of 140.5 +- 41.0 keV (chi squared 27.79 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 3.4 +- 0.0 x 10^-05 erg/cm2 and the 1-sec peak flux measured from T+76.05 sec in the 15-150 keV band is 15.8 +- 0.5 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.68 +- 0.03 (chi squared 43.74 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/1253910
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