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GCN Circular 15083

Subject
GRB 130807A, Swift-BAT refined analysis
Date
2013-08-08T14:35:14Z (10 years ago)
From
Hans Krimm at NASA-GSFC <hans.krimm@nasa.gov>
C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU),
A. Melandri (INAF-OAB), D. M. Palmer (LANL), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (MSU) (i.e. the Swift-BAT team):

Using the data set from T-60 to T+243 sec from the recent telemetry 
downlink,
we report further analysis of BAT GRB 130807A (trigger #565651)
(Melandri, et al., GCN Circ. 15082).  The BAT ground-calculated position is
RA, Dec = 269.801, -27.616 deg, which is
    RA(J2000)  =  17h 59m 12.4s
    Dec(J2000) = -27d 36' 56.7"
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 92%.

Based on the currently available event data, the mask-weighted light 
curve shows an initial FRED-like peak starting at T-10 sec, peaking at 
T=0 sec and decaying to background by T+50 sec.  This is followed by at 
least two more weaker peaks, one from roughly T+90 sec to T+130 sec and 
the second beginning at T+160 sec and continuing until the data cuts off 
at T+243 seconds.  The two later peaks are coincident with flares seen 
in the Swift/XRT data.  We note also that the Swift satellite slewed 
away from the source location at ~T+300 seconds, while an XRT flare was 
still ongoing. Since we do not have all of the data, we cannot determine 
T90 at this time.

The time-averaged spectrum from T-12.18 to T+163.82 sec is best fit by a 
power law with an exponential cutoff.  This fit gives a photon index 
0.31 +- 0.89,
and Epeak of 75.9 +- 35.2 keV (chi squared 56.96 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.2 +- 0.2 x 10^-06 
erg/cm2
and the 1-sec peak flux measured from T-4.68 sec in the 15-150 keV band is
0.4 +- 0.1 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.46 +- 0.17 (chi squared 63.40 for 57 d.o.f.).  All the quoted errors
are at the 90% confidence level.

The current analysis of the BAT data does not allow us to distinguish 
between the interpretations of this event as either a GRB or galactic 
transient. These results will be updated as more event data becomes 
available.

Examination of archival images from the Swift/BAT transient monitor 
through 3:03 UT, August 6, 2013 (~31.5 hours before the trigger) shows 
no sign of earlier emission from the location of trigger 565651.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/565651/BA/
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