TITLE:   GCN CIRCULAR
NUMBER:  20287
SUBJECT: GRB 161218A: POLAR observation
DATE:    16/12/18 18:58:48 GMT
FROM:    Zhengheng Li at POLAR  <lizhengheng@ihep.ac.cn>

Z. H. Li (IHEP), Y. H. Wang (IHEP), S. L. Xiong (IHEP) 
report for the POLAR collaboration:

At��2016-12-18T03:47:34.634��UT��(T0),��during��a��routine��on-ground��
search��of��data,��POLAR��detected the GRB 161218A,��
which��was��also��detected��by��the��Swift/BAT (trigger #727288).

The��POLAR��light��curve��consists��of��a single��peak,
with��a��duration��(T90) of��6.76��s��measured��from��T0+0.25��s .
The��0.25s��peak��rate��measured��from��T0+1.25��s��is��2660��cnts/s,
The��total��counts��is��about��6644 cnts.  The��above��measurements��are
in��the��energy��range��of��about��80-500��keV.

The preliminary estimation of minimum detectable polarization (MDP) 
is 32.5%[3-sigma, statistical only]. Follow-up observations are 
strongly encouraged.

LC_URL:
http://polar.ihep.ac.cn/grb/2016/GRB161218A/lc/POLAR_lc_grb161218158.png

Using��the��best��location��from��the��Fermi/GBM,��which��is��(J2000):
RA:������ 245.257����   [deg]
Dec:����  -4.114����   [deg]
Err:����������3.00      [arcmin]

the��incident��angle��in��POLAR��coordinate��at��T0��is:
theta:�� 24.327 ��[deg]
phi: ����356.614�� [deg]

The��analysis��results��presented��above��are��preliminary.

POLAR is a dedicated Gamma-Ray Burst polarimeter (50-500 keV) on-board 
the Chinese space laboratory Tiangong-2 launched on Sep 15, 2016. More 
information about POLAR can be found at http://polar.ihep.ac.cn/en/ , 
http://isdc.unige.ch/polar/ and http://polar.psi.ch/html/ .