GCN Circular 15076

A. Y. Lien (NASA/GSFC/ORAU), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), B.P. Gompertz (U Leicester), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC), 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-61 to T+242 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 130806A (trigger #565562)
(Gompertz, et al., GCN Circ. 15071
Not found
 
 
).  The BAT ground-calculated position is
RA, Dec = 35.907, 67.525 deg which is
     RA(J2000)  =  02h 23m 37.7s
     Dec(J2000) = +67d 31' 30.5"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 95%.

The mask-weighted light curves shows a faint initial 2-sec long peak
starting at T-5 sec, followed by the main peak from T-1 to T+2 sec.
T90 (15-350 keV) is 6.1 +- 0.5 sec (estimated error including systematics).

The time-averaged spectrum from T-4.5 to T+2.2 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.50 +- 0.22.  The fluence in the 15-150 keV band is 1.7 +- 0.2 x 10^-07
erg/cm2. The 1-sec peak photon flux measured from T+0.32 sec in the 15-150 keV
band is 1.3 +- 0.1 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/565562/BA/

We note that the fluence ratio in a simple power-law fit between the
25-50 keV band and the 50-100 keV band is 1.41.  This fluence ratio is larger
than 1.32 which can be achieved in the Band function of alpha=-1.0, beta=-2.5,
and Epeak=30 keV.  Thus, preliminary analysis shows that Epeak of the burst
is very likely around or below 30 keV.  Therefore the burst can be classified
as an X-ray flash (e.g. Sakamoto et al. 2008, ApJ, 679, 570).  A fit to a Band
model gives nearly the same reduced chi-squared as a simple power=law fit.  The
Band fit gives Epeak = 18.9 (+3.2, -5.8) and beta = -2.6 � 0.3.  The alpha
parameter is not constrained by the fit.