[vsnet-grb-info 7803] GRB 090509, further Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9349
SUBJECT: GRB 090509, further Swift-BAT refined analysis
DATE:    09/05/11 17:15:49 GMT
FROM:    Hans Krimm at NASA-GSFC  <hans.krimm at nasa.gov>

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), and J. R. Cummings (GSFC/UMBC) 
for the Swift-BAT team.

Here we report on further analysis of GRB 090509 (Grupe et al., GCN Circ. 9325) 
based on additional event data received since GCN Circ. 9335 (Tueller et al.) 
was issued.  The results given here supersede those from GCN Circ. 9335.

Using the data set from T-239 to T+316 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090509 (trigger #351525). The BAT 
ground-calculated position is
RA, Dec = 241.422, -28.385 deg which is
    RA(J2000)  =  16h 05m 41.3s
    Dec(J2000) = -28d 23' 04.4"
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 29%.

The mask weighted light curve consists of two sets of peaks widely separated in 
time.  The first complex contains multiple overlapping peaks starting at ~T-4 
sec, peaking at ~T+21 sec, and ending at ~T+40 sec.  The second complex also 
contains multiple overlapping peaks starting at ~T+240 sec, peaking at ~T+250 
sec and continuing until at least ~T+300 sec, when a pre-planned slew caused the 
source to move out of the BAT field of view.  However until ~T+950 sec the 
source was at a location outside the field of view where high energy (> 50 keV) 
photons from the source could have penetrated the BAT shield and contributed to 
the non-maskweighted light curve.  Examination of the raw light curve shows no 
additional peaks comparable in intensity to those described above.  We cannot 
rule out weak source activity or activity below about 50 keV. Based on the 
available data, T90 (15-350 keV) is 335 +- 32 sec (estimated error including 
systematics).

The time-averaged spectrum from T-62.6 to T+298.7 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.75 +- 0.20.  The fluence in the 15-150 keV band is 3.3 +- 0.4 x 10-6 erg/cm2.
The 1-sec peak photon flux measured from T+20.73 sec in the 15-150 keV band
is 1.5 +- 0.3 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/351525/BA/