TITLE: GCN CIRCULAR NUMBER: 20331 SUBJECT: GRB 161219B: POLAR Observation DATE: 16/12/22 10:38:13 GMT FROM: Haulin Xiao at PSI/POLAR Hualin Xiao (PSI), Wojtek Hajdas (PSI) and Radek Marcinkowski (PSI) report on behalf of the POLAR collaboration: At 2016-12-19T18:48:39.0 UT(T0), during a routine on-ground search of data, POLAR detected the GRB 161219B, which was also observed by Swift BAT (trigger #727541). The POLAR light curve consists of one peak with duration (T90) of 4.0 +- 0.5 s measured from T0. The 0.5 s peak flux at T0+1.75 s is equal to 248 +-44 cnts/sec. Above measurements are in the energy range of about 80 - 500 keV. LC_URL: http://polar.psi.ch/triggers/GRB161219B.png and http://polar.psi.ch/pub/lc.php?event=GRB+161219B Using the best location from the Swift BAT, which is (J2000): RA: 91.717 [deg] Dec: -26.790 [deg] the incident angle in the POLAR coordinate at T0 is: Theta: 96.6 [deg] Phi: 201.2 [deg] The analysis results presented above are preliminary. Calibration of the instrument is ongoing. POLAR is a dedicated Gamma-Ray Burst polarimeter which was launched on-board the Chinese space laboratory Tiangong-2 (TG-2) on Sep 15, 2016. The energy detection range of POLAR is ~ 50-500 keV. More information about POLAR can be found at http://polar.psi.ch/pub , http://polar.ihep.ac.cn/en/ and http://isdc.unige.ch/polar/ . This message is quotable in publications.