[vsnet-grb-info 11337] GRB 111228A, Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12749
SUBJECT: GRB 111228A, Swift-BAT refined analysis
DATE:    11/12/29 01:16:35 GMT
FROM:    Hans Krimm at NASA-GSFC  <hans.a.krimm at nasa.gov>

J. R. Cummings (GSFC/UMBC),S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (GSFC/UMBC), M. Stamatikos (OSU), J. Tueller (GSFC),
T. N. Ukwatta (MSU) (i.e. the Swift-BAT team):

Using the data set from T-239 to T+746 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 111228A (trigger #510649)
(Ukwatta, et al., GCN Circ. 12737).  The BAT ground-calculated position is
RA, Dec = 150.063, 18.284 deg which is
     RA(J2000)  =  10h 00m 15.0s
     Dec(J2000) = +18d 17' 02.2"
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 39%.

The mask-weighted light curve shows multiple peaks in several clusters.  The first
set of peaks is at a low level from T-12 s to T+12 s.  There is another low level
set from T+32 to T+42 s, followed by a much brighter set of three overlapping peaks
from T+45 to T+60 s. The final cluster is broad and relatively soft from T+85
to T+110 s. T90 (15-350 keV) is 101.20 +- 5.42 sec (estimated error including
systematics).

The time-averaged spectrum from T-12.82 to T+115.43 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.27 +- 0.06.  The fluence in the 15-150 keV band is 8.5 +- 0.2 x 10^-6  erg/cm2.
The 1-sec peak photon flux measured from T+54.56 sec in the 15-150 keV band
is 12.4 +- 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/510649/BA/