GRB 151227B

K. Senuma, A. Yoshida, T. Sakamoto, I. Takahashi, Y. Kawakubo, 
M. Moriyama, Y. Yamada (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), 
Y. Asaoka, S. Ozawa, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), 
M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena) 
and the CALET collaboration:

The long-duration GRB 151227B (Toelge et al. GCN Circ. 18727
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 ; Hurley et al. GCN Circ. 18773
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 ; 
Golenetskii et al. GCN Circ. 18781
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 ) triggered the CALET Gamma-Ray Burst Monitor (CGBM) at 
5:13:49.89 UT on 27 December 2015.  The clear burst signal was detected by HXM1 and SGM 
instruments.  

The light curve of the SGM shows three main peaks.  The first peak starts at T0, 
peaks at T0+2 sec and ends at T0+4 sec.  The brightest second peak, which consists 
of various sub-peaks, starts at T0+20 sec, peaks at T0+31 sec and ends at T0+40 sec.  
The third peak starts at T0+40 sec, peaks at T0+45 sec and ends at T0+50 sec.  
The T90 duration measured by the SGM data is 42.0 +- 0.3 sec (40-1000 keV).  

The CGBM data used in this analysis are provided by the Waseda CALET Operation Center 
located at the Waseda University.

S. Golenetskii, R.Aptekar, D. Frederiks, P. Oleynik, M. Ulanov,
D. Svinkin, A. Tsvetkova, A. Lysenko, A. Kozlova and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration, intense GRB 151227B
(Fermi GBM detection: Toelge & Bissaldi, GCN 18727
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 ;
IPN Triangulation: Hurley et al., GCN 18773
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 )
triggered Konus-Wind at T0=18827.479 s UT (05:13:47.479).

The burst light curve shows three emission episodes with a total 
duration of ~48 s.
The emission is seen up to ~15 MeV.

As observed by Konus-Wind, the burst
had a fluence of 6.49(-0.72,+0.72)x10^-5 erg/cm2,
and a 64-ms peak energy flux, measured from T0+29.728 s,
of 1.11(-0.20,+0.19)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+43.776 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.19(-0.08,+0.10),
the high energy photon index beta = -2.11(-0.18,+0.11),
the peak energy Ep = 228(-40,+46) keV,
chi2 = 110/97 dof.

The spectrum near the peak count rate
(measured from T0+24.832 to T0+35.584 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.25(-0.05,+0.05),
the high energy photon index beta = -2.57(-1.09,+0.28),
the peak energy Ep = 353(-44,+52) keV,
chi2 = 111/93 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB151227_T18827/

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.

K. Hurley, on behalf of the IPN,

I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin,
on behalf of the HEND-Odyssey GRB team,

S. Golenetskii, R. Aptekar, D. Frederiks, D. Svinkin,
and T. Cline on behalf of the Konus-Wind team,

V. Connaughton, M. S. Briggs, C. Meegan, V. Pelassa,
and A. Goldstein, on behalf of the Fermi GBM team,

A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo,
and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,

S. Barthelmy, J. Cummings, N. Gehrels, H. Krimm, and D. Palmer,
on behalf of the Swift-BAT team, and

W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr,
on behalf of the GRS-Odyssey GRB team, report:

The long-duration GRB 151227B has been detected by Fermi (GBM: Toelge 
and Bissaldi, GCN Circ. 18727
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 ), Konus-Wind, Mars-Odyssey (HEND), 
INTEGRAL (SPI-ACS), and Swift (BAT), so far, at about 18829 s UT 
(05:13:49). The burst was outside the coded field of view of the BAT.

We have triangulated it to a preliminary, 3 sigma error box whose 
coordinates are:
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   290.284 (19h 21m 08s) +35.415 (+35d 24' 55")
  Corners:
   290.279 (19h 21m 07s) +35.990 (+35d 59' 22")
   290.052 (19h 20m 13s) +36.037 (+36d 02' 12")
   290.288 (19h 21m 09s) +34.841 (+34d 50' 26")
   290.512 (19h 22m 03s) +34.792 (+34d 47' 32")
  ---------------------------------------------
The error box area is 759 sq. arcmin, and its maximum
dimension is 1.3 deg (the minimum one is 10.4 arcmin).
The Sun distance was 60 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB151227_T18827/IPN/

The Konus-Wind time history and spectrum will be given in a forthcoming 
GCN Circular.

Kilian Toelge (MPE) and Elisabetta Bissaldi (Politecnico di Bari) 
report on behalf of the Fermi GBM Team: 


"At 05:13:48.86 UT on 27 December 2015, the Fermi Gamma-Ray Burst Monitor 
triggered and located GRB 151227B (trigger 472886032 / 151227218). 
The on-ground calculated location, using the GBM trigger data, 
is RA = 287.9, DEC = 31.9 (J2000 degrees, 
equivalent to 19h 11m, 31d 54'), with an uncertainty 
of 1 degree (radius, 1-sigma containment, 
statistical only; there is additionally a systematic error 
which we have characterized as a core-plus-tail model, with 90% of 
GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg 
systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ). 

The angle from the Fermi LAT boresight at the GBM trigger time is 90 degrees. 

The GBM light curve consists of three pulses 
with a duration (T90) of about 43.0 s (50-300 keV). 
The time-averaged spectrum from T0+20.0 s to T0+49.7 s 
is best fit by a Band function with Epeak = 310 +/- 21 keV, 
alpha = -1.27 +/- 0.02, and beta = -2.17 +/- 0.08. 

The event fluence (10-1000 keV) in this time interval 
is (8.94 +/- 0.09)E-6 erg/cm^2. The 1-sec peak photon flux measured 
starting from T0+29.8 s in the 8-1000 keV band 
is 36.1 +/- 0.5 ph/s/cm^2.


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