TITLE:   GCN CIRCULAR
NUMBER:  20288
SUBJECT: GRB 161218B: POLAR observation
DATE:    16/12/18 19:04:42 GMT
FROM:    Yuanhao Wang at IHEP/CAS  <wangyuanhao@ihep.ac.cn>

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

At��2016-12-18T08:32:41.341��UT��(T0),��during��a��routine��on-ground��
search��of��data,��POLAR��detected the GRB 161218B,��which��was��also
detected��by��the Fermi/GBM (trigger 503742764/161218356).

The��POLAR��light��curve��consists��of��multiple��peaks,
with��a��duration��(T90) of��26.28��s��measured��from��T0+1.0��s .
The��1s��peak��rate��measured��from��T0+1.25��s��is��9849��cnts/s,
The��total��counts��is��about��29340 cnts.The��above��measurements��are
in��the��energy��range��of��about��80-500��keV.

The preliminary estimation of minimum detectable polarization(MDP) 
is 36.8%[3-sigma, statistical only]. Follow-up observations are 
strongly encouraged.

LC_URL:
http://polar.ihep.ac.cn/grb/2016/GRB161218B/lc/POLAR_lc_grb161218356.png

Using��the��best��location��from��the��Fermi/GBM,��which��is��(J2000):
RA:    358.640     [deg]
Dec:   -16.950     [deg]
Err:     1.00      [deg]

the��incident��angle��in��POLAR��coordinate��at��T0��is:
theta:�� 77.7612 ��[deg]
phi: ����252.239�� [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/