GCN Circular 20418

R. Marcinkowski (PSI), H. Xiao (PSI) and W. Hajdas (PSI) report on behalf 
of the POLAR collaboration:

At 2017-01-09 03:17:35 UT(T0), during a routine on-ground search of data, 
POLAR detected the GRB 170109A, which was also observed by Fermi GBM 
(trigger # 505624660). Significant detection was recorded in 5 of 25 
POLAR detection modules.

The POLAR light curve consists of multipeak structure compatible with Fermi 
GBM with duration (T90) of 9.0 +/- 1.0 s measured from T0. The 1.0 s peak 
flux at T0 + 4.5 s  is equal to 530 +/- 60 counts/sec. POLAR (5 modules) 
recorded 3140 +/- 140 events from the burst.

Above measurements are in the energy range of about 80 - 500 keV.

LC_URL: http://polar.psi.ch/triggers/GRB_170109A_raw_5of25.png
     or http://polar.psi.ch/pub/lc.php?event=GRB+170109A

Using the best location from the Fermi GBM, which is (J2000):

RA : 114.4  [deg]
Dec:  -6.8  [deg]
Err:   2.85 [deg]

the incident angle in the POLAR coordinate at T0 is:
Theta: 81.0 [deg]
Phi:  114.3 [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.