TITLE:   GCN CIRCULAR
NUMBER:  14419
SUBJECT: GRB 130420A, Swift-BAT refined analysis
DATE:    13/04/20 19:33:42 GMT
FROM:    Jay R. Cummings at NASA/GSFC/Swift  <james.r.cummings@nasa.gov>

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
http://gcn.gsfc.nasa.gov/notices_s/553977/BA/