TITLE: GCN CIRCULAR NUMBER: 20287 SUBJECT: GRB 161218A: POLAR observation DATE: 16/12/18 18:58:48 GMT FROM: Zhengheng Li at POLAR 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/ .