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GCN Circular 12130

Subject
GRB 110709B: Preliminary Swift-BAT refined analysis
Date
2011-07-10T01:47:27Z (13 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
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), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC),
G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
 
We report further analysis of BAT GRB 110709B (triggers #456967 and #456969;
Cummings, et al., GCN Circ. 12122 and Barthelmy, et al., GCN Circ. 12124).

Because of the interesting nature of this event, we are posting preliminary
versions of the "refined" processing on the two triggers of GRB 110709B.
The automated analysis of each trigger is provided separately.  We will likely
post the final refined analysis later when all of the full data is downlinked,
and the combined analysis can be performed.

At present, the first of the two BAT triggers (trigger #456967) consists 
of data from T-61 to T+234 sec.  The second trigger (trigger #456969) consists
of only a small amount of data from T-11 to T+63 sec.  The two triggers
are 645 sec apart.

The BAT ground-calculated position of the first trigger (#456967) is,
RA, Dec = 164.668, -23.470 deg, which is 
   RA(J2000)  =  10h 58m 40.3s 
   Dec(J2000) = -23d 28' 11.4" 
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 57%.   The position derived from the second trigger 
(#456969) is RA, Dec = 164.664, -23.500 deg, which is 
   RA(J2000)  =  10h 58m 39.4s 
   Dec(J2000) = -23d 29' 59.6" 
with an uncertainty of 3.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100% (on the BAT bore sight as a result of the
slew from the first trigger).  The two positions are separated by
1.8 arcmin.

The mask-weighted light curve of the first trigger, trigger #456967, 
shows the first peak of the cluster of peaks starting at ~T-30 sec
(note that the partial downlinked data start only at T-61 sec),
peaks at ~T+15 sec, and ends at T+130 or T+170 sec.
T90 (15-350 keV) is 55.6 +- 3.2 sec (estimated error including systematics).
 
The time-averaged spectrum of the data for the first trigger, trigger
#456967, from T-27.4 to T+46.7 sec is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.29 +- 0.04.
The fluence in the 15-150 keV band is 9.4 +- 0.2 x 10-6 erg/cm2.
The 1-sec peak photon flux measured from T+13.59 sec in the 15-150 keV band
is 3.4 +- 0.3 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 

The mask-weighted light curve of the second trigger, #456969, 
shows emission starting some time before the current data set
starting at T=21:43:25.4 - 11 sec  and extending beyond the
T=21:43:25.4 + 63 sec of the partially downlinked data.
 
The time-averaged spectrum of the second trigger, #456969, 
from T-8.2 to T+52.8 sec is best fit by a power law with an
exponential cutoff.  This fit gives a photon index 1.08 +- 0.17, 
and Epeak of 171.5 +- 81.8 keV (chi squared 36.6 for 56 d.o.f.).
A fit to a simple power law gives a photon index of 1.39 +- 0.04
(chi squared 47.2 for 57 d.o.f.).  All the quoted errors are
at the 90% confidence level. 
 
The results of the batgrbproduct analysis are available at
  Trigger 456967:  http://gcn.gsfc.nasa.gov/notices_s/456967/BA/
  Trigger 456969:  http://gcn.gsfc.nasa.gov/notices_s/456969/BA/
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