TITLE:   GCN CIRCULAR
NUMBER:  9064
SUBJECT: GRB 090401, Swift-BAT refined analysis
DATE:    09/04/01 05:39:25 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>

G. Sato (ISAS), 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/UMD), D. M. Palmer (LANL),
A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), P. Schady (MSSL-UCL),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+713 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090401 (trigger #348128)
(Schady, et al., GCN Circ. 9062).  The BAT ground-calculated position is
RA, Dec = 350.920, 29.762 deg, which is 
   RA(J2000)  =  23h 23m 40.8s 
   Dec(J2000) = +29d 45' 44.1" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 38%.
 
The mask-weighted light curve starts out at T-20 sec when the burst location
first came into the BAT FOV during a planned-target slew maneuver.  There is
evidence for emission starting prior to burst coming to the FOV.  There are
two small peaks at T+0 and T+30 sec. Then comes the main emission
with a series of at least 7 overlapping peaks starting at ~T+95 sec and
returning to background at ~T+190 sec.  T90 (15-350 keV) is 112 +- 15 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-9.4 to T+160.0 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.70 +- 0.05.  The fluence in the 15-150 keV band is 1.1 +- 0.0 x 10^-5 erg/cm2.
The 1-sec peak photon flux measured from T+122.05 sec in the 15-150 keV band
is 10.9 +- 0.5 ph/cm2/sec.  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/348128/BA/