GRB 090531***A***, Swift-BAT refined analysis
 
<somebody goes first>
<add the BA alphabetically>
S. D. Barthelmy (GSFC), 
W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA),
A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC),
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-487 to T+603 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090531***A*** (trigger #353627)
(NAME, et al., GCN Circ. xxxx).  The BAT ground-calculated position is
RA, Dec = 178.664, 7.830 deg which is 
   RA(J2000)  =  11h 54m 39.4s 
   Dec(J2000) = +07d 49' 46.8" 
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 73%.
 
[Description about the mask-weighted light curve]
T90 (15-350 keV) is 42.8 +- 8.1 sec (estimated error including systematics).
 
The time-averaged spectrum from T-25.5 to T+34.6 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.94 +- 0.42, 
and Epeak of 78.6 +- 34.4 keV (chi squared 66.13 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.5 +- 0.1 x 10^-06 erg/cm2
and the 1-sec peak flux measured from T+9.29 sec in the 15-150 keV band is
1.2 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.58 +- 0.10 (chi squared 73.83 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/353627/BA/