GRB 130420A, Swift-BAT refined analysis
A. Y. Lien (NASA/GSFC/ORAU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), M. J. Page (UCL-MSSL),
D. M. Palmer (LANL), T. Sakamoto (AGU), G. Sato (ISAS), M. Stamatikos (OSU),
J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+303 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 130420A (trigger #553977)
(Page et al., GCN 14406). The BAT ground-calculated position is
RA, Dec = 196.118, 59.421 deg which is
RA(J2000) = 13h 04m 28.3s
Dec(J2000) = +59d 25' 16.8"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 86%.
The mask-weighted light curve shows a precursor beginning gradually at about
T-20 seconds and increasing irregularly to about T+100 seconds. The main
emission had a FRED shape peaking at about T+110 seconds that was detectable
until about T+200 seconds. T90 (15-350 keV) is 123.5 +- 13.1 sec (estimated
error including systematics).
The time-averaged spectrum from T-19.7 to T+189.9 sec is best fit by a power law
with an exponential cutoff. This fit gives a photon index 1.52 +- 0.25,
and Epeak of 33.2 +- 6.8 keV (chi squared 42.40 for 56 d.o.f.). For this
model the total fluence in the 15-150 keV band is 7.1 +- 0.3 x 10^-06 erg/cm2
and the 1-sec peak flux measured from T+110.67 sec in the 15-150 keV band is
3.4 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index
of 2.18 +- 0.05 (chi squared 66.06 for 57 d.o.f.). All the quoted errors
are at the 90% confidence level.
The results of the batgrbproduct analysis are available at