GRB 131226A

S. R. Oates (UCL-MSSL), H. A. Krimm (CRESST/GSFC/USRA),
N. P. M. Kuin (UCL-MSSL) and M. H. Siegel (PSU) report on behalf of
the Swift Team:

At 05:47:39 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 131226A (trigger=582123).  
The BAT on-board calculated location is 
RA, Dec 301.307, -64.962 which is 
   RA(J2000) = 20h 05m 14s
   Dec(J2000) = -64d 57' 43"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 10 sec.  The peak count rate
was ~15000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

Due to a Sun observing constraint, Swift cannot slew to the BAT
position until 2014 January 27. There will thus be no XRT or
UVOT data for this trigger. 

Burst Advocate for this burst is S. R. Oates (samantha.oates AT ucl.ac.uk). 
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.)

M. Stamatikos (OSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
A. Y. Lien (NASA/UMBC), C. B. Markwardt (GSFC), S. R. Oates (UCL-MSSL),
D. M. Palmer (LANL), T. Sakamoto (AGU), J. Tueller (GSFC),
T. N. Ukwatta (MSU) (i.e. the Swift-BAT team):

Using the data set from T-239 to T+481 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 131226A (trigger #582123)
(Oates, et al., GCN Circ. 15612
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 ).  The BAT ground-calculated position is
RA, Dec = 301.309, -64.943 deg which is
    RA(J2000)  =  20h 05m 14.2s
    Dec(J2000) = -64d 56' 35.2"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 56%.

The mask-weighted light curve shows a very complex structure with more than a 
dozen peaks covering the time period from T-0.5 sec to T+8.5 sec and peaking at 
T+1 sec.  This is followed by lower-level extended emission out to ~T+180 sec. 
T90 (15-350 keV) is 7.20 +- 0.16 sec (estimated error including systematics).

The time-averaged spectrum from T-0.26 to T+8.42 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.38 +- 0.04.  The fluence in the 15-150 keV band is 4.0 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+1.11 sec in the 15-150 keV band
is 10.4 +- 0.4 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/582123/BA/

S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf
of the Konus-Wind team, report:

The long-duration GRB 131226A (Swift-BAT trigger 582123: Oates, et al., 
GCN 15612
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 ; Stamatikos, et al. GCN 15613
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 ) triggered Konus-Wind at 
T0=20858.013 s UT (05:47:38.013).

The burst light curve shows a multi-peaked structure with a total 
duration of ~7 s.

As observed by Konus-Wind, the burst
had a fluence of 1.01(-0.07,+0.08)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+2.704 s,
of (5.0 +/- 1.0)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum (measured from T0 to T0+8.448 s)
is well fitted (in the 20 keV - 2 MeV range) by a power law with 
exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), with
alpha = -0.90(-0.12,+0.13),  and
Ep = 264(-17,+20) keV (chi2 = 65.6/60 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and only an upper limit on the high energy
photon index: beta < -2.5.

All the quoted values are preliminary.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB131226_T20858/