[vsnet-grb-info 13587] GRB 130612A: Swift-BAT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14916
SUBJECT: GRB 130612A: Swift-BAT refined analysis
DATE:    13/06/19 22:01:54 GMT
FROM:    Craig Markwardt at NASA/GSFC  <craigm at milkyway.gsfc.nasa.gov>

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC), T. Sakamoto (AGU),
on behalf of the Swift-BAT team:

Using the data set from T-25 to T+100 sec from the recent telemetry 
downlink, we report further analysis of BAT GRB 130612A (trigger 
#557976) (Racusin, et al., GCN Circ. 14874).  The BAT ground-calculated 
position is
RA, Dec = 259.771, 16.729 deg which is
    RA(J2000)  =  17h 19m 05.0s
    Dec(J2000) = +16d 43' 44.7"
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 34%.

The mask weighted light curve shows a single FRED-like profile with a 
rise time of about 1 sec near T+0sec and a gradual decay time with 
e-folding time of about 3 sec.  This burst was detected as the Swift 
spacecraft was entering the South Atlantic Anomaly region, and the raw 
background counting rate was ramping upward.  The mask weighted light 
curve does not have a clean background level, so estimating the T90 is 
difficult.  If we restrict the analysis to the time range T-25 to T+100, 
we estimate T90 (15-350 keV) to be 4.0 +/- 1.4 sec.  However, we cannot 
rule out the possibility of a faint extended emission tail to 
approximately T+100 (in which case T90 is 110 +/- 60 sec).

The time-averaged spectrum from T-0.83 to T+3.17 sec is best fit by a 
power law with an exponential cutoff.  This fit gives a photon index 
-0.14 +- 1.71,  and Epeak of 36.4 +- 7.6 keV (chi squared 36 for 56 
d.o.f.).  For this model the total fluence in the 15-150 keV band is 2.3 
+- 0.5 x 10^-7 erg/cm2 and the 1-sec peak flux measured from T+0.17 sec 
in the 15-150 keV band is 1.7 +- 0.3 ph/cm2/sec.  A fit to a simple 
power law gives a photon index of 2.06 +- 0.25 (chi squared 44 for 57 
d.o.f.).  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/557976/BA/