GRB 081101

M. Stamatikos (NASA/ORAU), S. D. Barthelmy (GSFC),
N. Gehrels (NASA/GSFC), N. P. M. Kuin (MSSL),
V. La Parola (INAF-IASFPA), C. B. Markwardt (CRESST/GSFC/UMD),
D. M. Palmer (LANL) and P. Romano (INAF-IASFPA) report on behalf of
the Swift Team:

At 11:46:31 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081101 (trigger=333320).  Swift did not slew because 
of the low merit value assignment because of the chance spatial coincidence
with the A0620-00 blackhole candidate source. 
The BAT on-board calculated location is 
RA, Dec 95.826, -0.082 which is 
   RA(J2000)  =  06h 23m 18s
   Dec(J2000) = -00d 04' 55"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single hard spike
with a duration of less than 128 msec.  The peak count rate
was ~7000 counts/sec (15-350 keV), at ~0 sec after the trigger. 
We can not rule out that this was from A0620-00, although the position 
is a very unlikely 18 arcmin away.  Thus, we believe this to be a gamma-ray
burst, or possibly a new SGR (although the spectrum is harder than typical
SGR bursts). 

Burst Advocate for this burst is M. Stamatikos (michael AT milkyway.gsfc.nasa.gov). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)

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
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 ).  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.

V. La Parola, V. Mangano, B. Sbarufatti (INAF-IASF PA)
report on behalf of the Swift-XRT team

We have analysed the Swift-XRT follow-up observation of the source
(trigger #333320; Stamatikos, et al., GCN Circ. 8457
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 )
started on 2008-11-01 14:49:13 UT (about 11 ks after the trigger).
In the first 3.4 ks of data no source is detected within the
BAT refined error circle (Barthelmy, et al., GCN Circ. 8458
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 )
down to a limiting flux of 1.4e-13 erg cm^-2 s^-1.

This is an official product of the Swift-XRT team.

A. von Kienlin (MPE), E. Bissaldi (MPE), M.S. Briggs (UAHuntsville) and C.
Kouveliotou (NASA/MSFC) report on behalf of the Fermi GBM Team: 

"At 11:46:32 UT on 01 November 2008, the Fermi GBM triggered and located an
event (trigger 247232793 / 081101491) which was also seen by SWIFT
(Stamatikos et al. 2008, GCN 8457
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 , Barthelmy et al. 2008, GCN 8458
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 ). The GBM
on-ground location is consistent with the Swift position.

The GBM light curve shows a single peak with duration of about 224 ms. The
event is significantly detected with GBM between 40 - 200 keV. The
time-averaged spectrum from T0-0.103 s to T0+0.121 s is best fit by a single
power law with index -1.14 +/- 0.07 (chi squared 212 for 234 d.o.f.). The
event fluence (50-300 keV) in the same time interval is (1.6 +/- 0.08) E-07
erg/cm^2. 

The Swift team suggested that the event could be a possible new Soft Gamma
Repeater (SGR 0623-0006). The GBM spectrum is more consistent with that of a
faint short GRB; the lack of photons below 40 keV is rather unusual for an
SGR. 

The spectral analysis results presented above are preliminary; final results
will be published in the GBM GRB Catalog."