GRB 181212A

C. L. Fletcher (USRA)

report on behalf of the Fermi GBM Team:



"At 16:37:46.05 UT on 12 December 2018, the Fermi Gamma-Ray Burst Monitor

triggered and located GRB 181212A (trigger 566325471 / 181212693).



The on-ground calculated location, using the GBM trigger

data, is RA = 298.4, DEC = -3.7 (J2000 degrees,

equivalent to 19 h 53 m 33.60 s, -03 d 42 '), with an uncertainty

of 2.3 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 114 degrees.



The GBM light curve consists of a bright pulse

with a duration (T90) of about 58 s (50-300 keV).

The time-averaged spectrum from T0+0 s to T0+58 s is

best fit by a Band function with Epeak = 72 +/- 8 keV,

alpha = -1.4 +/- 0.1, and beta = -2.2 +/- 0.1



The event fluence (10-1000 keV) in this time interval is

(2.138 +/- 0.052)E-05 erg/cm^2. The 1-sec peak photon flux measured

starting from T0+1.9 s in the 10-1000 keV band

is 66 +/- 1 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,

D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks, A. Kozlova
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,

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, 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 181212A
(Fermi-GBM detection: Fletcher, GCN Circ. 23524
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 )
was detected by Fermi (GBM trigger 566325471), Konus-Wind,
INTEGRAL (SPI-ACS), Mars-Odyssey (HEND), and Swift (BAT)
at about 59866 s UT (16:37:46).
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:
   300.663 (20h 02m 39s)  -0.324 ( +0d 19' 27")
  Corners:
   301.111 (20h 04m 27s)  +1.224 ( +1d 13' 26")
   300.707 (20h 02m 50s)  +1.563 ( +1d 33' 47")
   300.075 (20h 00m 18s)  -3.456 ( -3d 27' 22")
   300.497 (20h 01m 59s)  -3.868 ( -3d 52' 05")
  ---------------------------------------------
The error box area is about 2.31 sq. deg, and its maximum
dimension is 5.43 deg (the minimum one is 29 arcmin).
The Sun distance was about 43 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB181212_T59862/IPN

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

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

The long GRB 181212A (IPN Triangulation: Hurley et al., GCN 23534
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 ;
Fermi-GBM detection: Fletcher, GCN 23524
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 )
triggered Konus-Wind at T0=59862.922 s UT (16:37:42.922).

The burst light curve shows a single bright pulse followed
by a weaker extended emission.
The total duration of the burst (T90, 80-1300 keV) is ~66 s.
The emission in the main peak is seen up to ~10 MeV.

As observed by Konus-Wind, the burst had a fluence of
(2.4 �� 0.5)x10^-5 erg/cm2 and a 64-ms peak energy flux,
measured from T0+1.536 s, of (1.02 �� 0.13)x10^-5 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+72.448 s)
is best fit in the 20 keV - 15 MeV range by a cutoff power-law
(CPL) function with the following model parameters:
the photon index alpha = -1.75(-0.08,+0.08),
and the peak energy Ep = 216(-45,+84) keV,
chi2 = 100/98 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep, and only an upper limit on beta (<-2.3).

The spectrum near the peak count rate (measured from T0
to T0+6.912 s) is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.55 (-0.12,+0.09),
the high energy photon index beta = -2.38 (-7.62,+0.14),
the peak energy Ep = 158 (-20,+47) keV,
chi2 = 101/95 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB181212_T59862/

All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.

S. Xiao, C. K. Li, X. B. Li, G. Li, J. Y. Liao, S. L. Xiong, 
C. Z. Liu, X. F. Li, Z. W. Li, Z. Chang, X. F. Lu, J. L. Zhao,
A. M. Zhang, Y. F. Zhang, C. L. Zou (IHEP), Y. J. Jin, 
Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, 
H. Y. Wang, M. Wu, Y. P. Xu, S. N. Zhang (IHEP), 
report on behalf of the Insight-HXMT team: 
At 2018-12-12T16:37:45.500 (T0), the Insight-HXMT/HE detected 
GRB 181212A (trigger ID: HEB181212692) in a routine search of the data, 
which was also triggered by Fermi/GBM (Fletcher et al., GCN23524
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 ) and
Konus-Wind (Frederiks et al., GCN23540
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 ).
The Insight-HXMT/HE light curve mainly consists of single 
pulse with a duration (T90) of 5.48 s measured from T0+0.72 s. 
The 1-s peak rate, measured from T0+2.07 s, is 8019.2 cnts/s. 
The total counts from this burst is 20371.7 counts. 
URL_LC: http://www.hxmt.org/images/GRB/HEB181212692_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 (record 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 
fundedjointly by the China National Space Administration (CNSA) and 
the Chinese Academy of Sciences (CAS). 
More information could be found at: http://www.hxmt.org.