J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (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 150428B (trigger #639278)
(Page, et al., GCN Circ. 17766). The BAT ground-calculated position is
RA, Dec = 292.661, 4.114 deg which is
RA(J2000) = 19h 30m 38.8s
Dec(J2000) = +04d 06' 52.2���
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 40%.
The mask-weighted light curve shows three peaks. The first peak starts at T-40 sec,
peaks at T-25 sec and ends at T-20 sec. The second peak starts at T-15 sec, peaks
at T+5 sec and ends at T+50 sec. And the third peak starts at T+55 sec, peaks at T+65 sec
and ends at T+120 sec. T90 (15-350 keV) is 130.9 +- 15.6 sec
(estimated error including systematics).
The time-averaged spectrum from T-40.1 to T+121.7 sec is best fit by a power law
with an exponential cutoff. This fit gives a photon index 1.0 +- 0.5, and Epeak
of 55 +- 10 keV (chi squared 37.44 for 56 d.o.f.). For this model the total
fluence in the 15-150 keV band is 3.7 +- 0.3 x 10^-6 erg/cm2 and the 1-sec peak flux
measured from T+1.36 sec in the 15-150 keV band is 1.5 +- 0.3 ph/cm2/sec. A fit
to a simple power law gives a photon index of 1.87 +- 0.10
(chi squared 49.44 for 57 d.o.f.). All the quoted errors are at the 90% confidence level.
The results of the batgrbproduct analysis are available at