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GCN Circular 12259

Swift SGR 1834.9-0846: Swift-BAT refined analysis
2011-08-08T11:40:09Z (13 years ago)
Scott Barthelmy at NASA/GSFC <>
S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC),
V. D'Elia (ASDC), 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):
Using the data set from T-240 to T+963 sec from recent telemetry downlinks,
we report further analysis of Swift SGR 1834.9-0846 (trigger #458907)
(which we reported as GRB 110807A in D'Elia, et al., GCN Circ. 12253).
The BAT ground-calculated position is RA, Dec = 278.709, -8.758 deg, which is 
   RA(J2000)  =  18h 34m 50.1s 
   Dec(J2000) = -08d 45' 28.4" 
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 89%.
The mask-weighted light curve shows a single spike starting at T_zero and
ending at ~T+0.04 sec.  T90 (15-350 keV) is 0.032 +- 0.008 sec
(estimated error including systematics).
The time-averaged spectrum from T+0.0 to T+0.040 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index -0.70 +- 2.57, 
and Epeak of 40.5 +- 8.0 keV (chi squared 51.9 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.2 +- 0.3 x 10^-8 erg/cm2
and the 1-sec peak flux measured from T-0.48 sec in the 15-150 keV band is
0.3 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 2.13 +- 0.30 (chi squared 59.7 for 57 d.o.f.).  All the quoted errors
are at the 90% confidence level. 

Given the soft nature of this event, the Fermi-GBM event consistant
with this location (Guiriec, 12255), and that the Swift location does not match
any of the known SGRs, we classify this event as a new SGR source.  The digits
in the name are derived from the Swift-XRT location (Circ 12253).
The results of the batgrbproduct analysis are available at
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