[vsnet-grb-info 8542] GRB 091020, Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10051
SUBJECT: GRB 091020, Swift-BAT refined analysis
DATE:    09/10/21 01:28:59 GMT
FROM:    Hans Krimm at NASA-GSFC  <hans.krimm at nasa.gov>

D. M. Palmer (LANL), 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), A. M. Parsons (GSFC),
J. L. Racusin (NASA/GSFC/ORAU), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):

Using the data set from T-61 to T+242 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 091020 (trigger #373458)
(Racusin, et al., GCN Circ. 10048).  The BAT ground-calculated position is
RA, Dec = 175.727, 50.977 deg which is
    RA(J2000)  =  11h 42m 54.4s
    Dec(J2000) = +50d 58' 36.6"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 43%.

The mask-weighted light curve began with a small hump at T-10 sec, rising
sharply to a peak at T+2 sec and decaying exponentially out to T+50 sec,
with a much smaller peak superimposed at T+30 sec. T90 (15-350 keV) is
34.6 +- 2.7 sec (estimated error including systematics).

The time-averaged spectrum from T-8.7 to T+38.3 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.53 +- 0.07.  The fluence in the 15-150 keV band is
3.7 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from
T+1.14 sec in the 15-150 keV band is 4.2 +- 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/373458/BA/