GRB 151222A

Hoi-Fung Yu (MPE) reports on behalf of the Fermi GBM Team:

"At 08:10:13.62 UT on 22 Dec 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 151222A (trigger 472464617 / 151222340).
The on-ground calculated location, using the GBM trigger data, 
is RA = 355, Dec = 36.7 (J2000 degrees, equivalent to 23h 40m, 36d 42'), 
with an uncertainty of 3 degrees (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 117 degrees.

The GBM light curve consists of two short pulses with a duration (T90) of 
about 0.8 s (50-300 keV). The time-averaged spectrum from T0-0.256 s 
to T0+0.768 s is best fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.68 +/- 0.09 and
the cutoff energy, parameterized as Epeak, is 1490 +/- 270 keV.

The event fluence (10-1000 keV) in this time interval is
(2.36 +/- 0.13)E-06 erg/cm^2. The 64-ms peak photon flux measured
starting from T0-0.256 s in the 10-1000 keV band
is 12.9 +/- 1.9 ph/s/cm^2.

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

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, V. Pal'shin, 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,
and

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

The short-duration, hard-spectrum GRB 151222A has been detected
by Konus-Wind, Fermi (GBM: Hoi-Fung Yu GCN Circ. 18715
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 ),
INTEGRAL (SPI-ACS), and Mars-Odyssey (HEND), so far,
at about 29414 s UT (08:10:14).

We have triangulated it to a preliminary, 3 sigma error box whose 
coordinates are:
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   354.942 (23h 39m 46s) +34.095 (+34d 05' 44")
  Corners:
   355.188 (23h 40m 45s) +34.534 (+34d 32' 01")
   354.558 (23h 38m 14s) +33.943 (+33d 56' 34")
   354.701 (23h 38m 48s) +33.652 (+33d 39' 07")
   355.328 (23h 41m 19s) +34.244 (+34d 14' 39")
  ---------------------------------------------
The error box area is 792 sq. arcmin, and its maximum
dimension is 58 arcmin (the minimum one is 16.8 arcmin).
The Sun distance was 98 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB151222_T29415/IPN/

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

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

The short-duration, hard-spectrum GRB 151222A
(Fermi GBM detection: Hoi-Fung Yu, GCN Circ. 18715
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 ;
IPN triangulation: Hurley, et al., GCN Circ. 18720
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 )
triggered Konus-Wind at T0=29415.138  s UT (08:10:15.138).

The burst light curve shows a double-peaked structure
with a total duration of ~0.5 s.

As observed by Konus-Wind, the burst
had a fluence of 2.20(-0.23,+0.28)x10^-6 erg/cm2
and a 16-ms peak flux, measured from T0+0.048 s,
of 1.03(-0.11,+0.13)x10^-5 erg/cm2/s
(both in the 20 - 1500 keV energy range).

Since a major fraction of the burst counts was accumulated
before the trigger, the spectral analysis was performed using
the KW 3-channel light curve data.
Modeling the 3-channel time-integrated spectrum
(measured from T0-0.434 s to T0+0.094 s)
by the cutoff power law yields the following model parameters:
the photon index alpha=0.13(-0.44,+0.64),
and the peak energy Ep=625(-118,+220) keV.

All the quoted errors are estimated at the 1 sigma confidence level.
All the presented results are preliminary.

The K-W light curve of this burst is available at
http://www.ioffe.ru/LEA/GRBs/GRB151222_T29415/