GRB 191227B

K. Hurley, on behalf of the IPN,

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

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

A. Goldstein, M. S. Briggs, and C. Wilson-Hodge
on behalf of the Fermi GBM team,

S. Barthelmy, J. Cummings, 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 very bright, short-duration GRB 191227B was detected by
Fermi (GBM trigger 599160109), Mars-Odyssey (HEND), Konus-Wind,
and Swift (BAT) at about 62504 s UT (17:21:44).
The burst was outside the coded field of view of the BAT.

We have triangulated it to two preliminary, 3 sigma error boxes
whose coordinates are:
Box 1:
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   256.466 (17h 05m 52s) -26.739 (-26d 44' 19")
  Corners:
   256.590 (17h 06m 22s) -26.856 (-26d 51' 20")
   256.273 (17h 05m 05s) -27.785 (-27d 47' 06")
   256.342 (17h 05m 22s) -26.619 (-26d 37' 09")
   256.724 (17h 06m 54s) -25.195 (-25d 11' 40")
  ---------------------------------------------

  Box 2:
  ---------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ---------------------------------------------
  Center:
   257.405 (17h 09m 37s) -19.765 (-19d 45' 52")
  Corners:
   257.550 (17h 10m 12s) -19.678 (-19d 40' 41")
   257.500 (17h 10m 00s) -18.708 (-18d 42' 29")
   257.260 (17h 09m 02s) -19.853 (-19d 51' 12")
   257.244 (17h 08m 59s) -21.319 (-21d 19' 08")
  ---------------------------------------------
The area of each error box is 1162 sq. arcmin,
and their maximum dimension is 2.62 deg
(the minimum one is 14.16 arcmin).
The Sun distance for each box was ~18 deg.

These error boxes are both consistent with the GBM localization.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB191227_T62500/IPN

The time history and spectrum will be given in forthcoming
GCN Circulars.

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

The short-duration GRB 191227B
(IPN triangulation: Hurley et al., GCN Circ. 26612
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triggered Konus-Wind at T0=62500.487 s UT (17:21:40.487).

The burst light curve shows a multi-peaked structure
which starts at ~T0 s and has a total duration of ~0.2 s.
The emission is seen up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB191227_T62500/

As observed by Konus-Wind, the burst
had a fluence of 8.80(-1.42,+1.40)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0+0.030 s,
of 8.83(-2.12,+2.10)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+0.192 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.56(-0.21,+0.31),
the high energy photon index beta = -2.35(-1.19,+0.38),
the peak energy Ep = 985(-323,+373) keV
(chi2 = 49/49 dof).

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

Y. F. Du, Y. G. Zheng, C. Cai, Q. Luo, S. Xiao, Q. B. Yi, 
Y. Huang, C. K. Li, G. Li, X. B. Li, J. Y. Liao, S. L. Xiong,
C. Z. Liu, X. F. Li, Z. W. Li, Z. Chang, A. M. Zhang, 
Y. F. Zhang, X. F. Lu, C. L. Zou (IHEP), Y. J. Jin, 
Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, 
M. Wu, Y. P. Xu, S. N. Zhang (IHEP), 
report on behalf of the Insight-HXMT team:

At 2019-12-27T17:21:44.14 (T0), Insight-HXMT/HE detected 
GRB 191227B (trigger ID: HEB191227723) in a routine search of the data, 
which was also triggered by Fermi/GBM, IPN and Konus-Wind (GCN #26612
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 ).

The Insight-HXMT/HE light curve mainly consists of multiple 
pulses with a duration (T90) of 0.161 s measured from T0+0.010 s. 
The 1-ms peak rate, measured from T0+0.045 s, is 50,544 cnts/sec. 
The total counts from this burst is 4123 counts. But it should be
noted that the Insight-HXMT/HE detection suffers from saturation 
when the count rate exceeds ~20,000 cnts/sec. The uncorrected 
light curve can be found at:
URL_LC: http://www.hxmt.org/images/GRB/HEB191227723_lc.jpg 

All measurements above are made with the CsI detectors operating in the 
regular mode with the energy range of about 80-800 keV (deposited energy). 
Only gamma-rays with energy greater than about 200 keV can penetrate 
the spacecraft and leave signals in the CsI detectors installed inside 
of the telescope. 

Insight-HXMT is the first Chinese space X-ray telescope, which was 
funded jointly by the China National Space Administration (CNSA) and 
the Chinese Academy of Sciences (CAS). 
More information about it could be found at: 
http://www.hxmt.org.