TITLE:   GCN CIRCULAR
NUMBER:  6342
SUBJECT: GRB 070420 Swift-BAT Refined Analysis
DATE:    07/04/21 02:16:48 GMT
FROM:    Michael Stamatikos at GSFC  <michael@milkyway.gsfc.nasa.gov>

A. Parsons (GSFC), L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings
(GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), D. Palmer (LANL), T. Sakamoto (GSFC/ORAU), G. Sato
(GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) on behalf of 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 070420 (trigger #276321)
(Stamatikos, et al., GCN Circ. 6330). The BAT ground-calculated position
is RA, Dec = 121.245, -45.564 deg which is 
   RA(J2000) = 8h 4m 58.7s 
   Dec(J2000) = -45d 33' 50.6" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The
partial coding was 8%.
 
The light curve is described by a slow rise to double-peaks at T+2 and T+8
sec, with subsequent gradual decay spanning from T-50 to T+70 sec. The T90
(15-350 keV) is 77 +- 4 sec (estimated error including systematics).
 
The time-averaged spectrum from T-29 to T+100 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.16 +- 0.24, and
Epeak of 114 +- 42 keV (chi squared 50.74 for 56 d.o.f.). For this model the
total fluence in the 15-150 keV band is 1.40 +- 0.04 x 10-5 erg/cm2 and the
1-sec peak flux measured from T+1.40 sec in the 15-150 keV band is 7.1 +-
0.8 ph/cm2/sec.  A fit to a simple power law gives a photon index of 
1.59 +- 0.05 (chi squared 61.25 for 57 d.o.f.).  All the quoted errors 
are at the 90% confidence level.