GCN Circular 8458

S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC),
C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), M. Stamatikos (GSFC/ORAU),
J. Kennea (PSU), V. Mangano (INAF-IASFPa), V. LaParola (INAF-IASFPA),
P. Romano (INAF-IASFPA), N. P. M. Kuin (MSSL)
(on behalf of the Swift-BAT/-XRT teams):
 
Using the data set from T-239 to T+963 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 081101 (trigger #333320)
(Stamatikos, et al., GCN Circ. 8457
Not found
 
 
).  The BAT ground-calculated position is
RA, Dec = 95.836, -0.112 deg, which is 
   RA(J2000)  =  06h 23m 20.7s 
   Dec(J2000) = -00d 06' 41.5" 
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 50%.
 
The mask-weighted light curve shows a single spike starting at ~T-0.05 sec,
peaking at ~T+0.1 sec, and ending by ~T+0.3 sec.
T90 (15-350 keV) is 0.20 +- 0.02 sec (estimated error including systematics).
 
The time-averaged spectrum from T+0.0 to T+0.2 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index -0.24 +- 1.12, 
and Epeak of 78 +- 34 keV (chi squared 62.8 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 6.2 +- 1.0 x 10^-8 erg/cm2
and the 1-sec peak flux measured from T-0.38 sec in the 15-150 keV band is
3.6 +- 0.5 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.25 +- 0.20 (chi squared 69.9 for 57 d.o.f.).  All the quoted errors
are at the 90% confidence level.

The BAT results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/333320/BA/

Swift/XRT began observing the field at 13:37:56 UT, 111 minutes after  
the BAT trigger, and observed the field in photon counting mode for 200 sec.
No point sources were detected in the field of view.  
Observations of this field are ongoing.

Given the short single spike form of the BAT lightcurve and the  
somewhat soft spectral values, this suggests that this is an SGR.
We can not rule out a GRB explanation of this event.