GCN Circular 20126

S. L. Xiong (IHEP), N. Produit (UniGe), T. W. Bao (IHEP), T. Batsch (NCBJ),
T. Bernasconi, F. Cadoux, I. Cernuda (UniGe), J. Y. Chai, Y. W. Dong, M.  Z. Feng (IHEP),
N. Gauvin (UniGe), M. Y. Ge (IHEP), W. Hajdas (PSI), J. J. He, Y. Huang (IHEP),
M. R. Kole (UniGe), M. N. Kong (IHEP), C. Lechanoine-Leluc (UniGe), H.  C. Li,
L. Li, Z. H. Li, J. T. Liu, X. Liu, F. J. Lu (IHEP), R. Marcinkowski (PSI), S. Orsi, M. Pohl,
D. Rapin (UniGe), A. Rutczynska, D. Rybka (NCBJ), H. L. Shi, L. M. Song, J. C. Sun (IHEP),
J. Szabelski (NCBJ), R. J. Wang, Y. H. Wang, X. Wen, B. B. Wu (IHEP), X.  Wu (UniGe),
H. L. Xiao (PSI), H. H. Xu, M. Xu, J. Zhang, L. Zhang, L. Y. Zhang (IHEP), P. Zhang (PSI),
S. N. Zhang, X. F. Zhang, Y. J. Zhang, Y. Zhao, S. J. Zheng (IHEP), A. 
Zwolinska (NCBJ)
(i.e. the POLAR team):

POLAR, a dedicated Gamma-Ray Burst polarimeter, has been launched successfully
on-board the Chinese space laboratory Tiangong-2 (TG-2) on Sep 15, 2016.

During the commissioning operation phase, at 19:48:05.00 UT on 28 
September 2016 (T0),
POLAR detected the GRB160928A in a routine ground search of the data,
which was also observed by the Fermi/GBM (trigger 496784887/160928825),
INTEGRAL/SPI-ACS (trigger #7579) and Konus-WIND (trig #4385).

POLAR can localize bursts within its FOV (~ half sky) to an accuracy of degrees
(Suarez-Garcia et al., NIM A, 2010, 624). However, since this burst is 
not very bright and
falls on the edge of the FOV, the localization is difficult and still on-going.

Using the best location from the Fermi/GBM, which is (J2000):
RA:   130.39    [deg]
Dec:    8.14    [deg]
Err:    3.19    [deg]

the incident angle at T0 in POLAR detector coordinate is:
theta:   94.7   [deg]
phi:    -26.8   [deg]

The distribution of the GRB signal among its 25 detector modules is 
consistent with this incident geometry.

In addition, the timing and structures in the POLAR light curve is well 
consistent with that of other instruments mentioned above.
Thus we conclude that this event is the first confirmed GRB which POLAR detected,
and that POLAR works as expected.

The POLAR light curve consists of multiple peaks
with a duration (T90) of 5.1 s measured from T0-1.7 s.
The 50-ms peak flux, measured from T0+0.55 s, is 1406.7 cnts/sec.
The above measurements are in the energy range of about 80-500 keV.

The analysis results presented above are preliminary;
final results will be published in the POLAR paper.

The POLAR mission is a joint effort of the international collaboration 
between the Institute of High Energy Physics (IHEP) in China, the University of 
Geneva (UniGe) and the Paul Scherrer Institute (PSI) in Switzerland, and the National 
Center for Nuclear Research (NCBJ) in Poland. More information about POLAR could be 
found at http://polar.ihep.ac.cn/en/.

[GCN OPS NOTE(05nov16):  Per author's request, the affiliation in the FROM:-line
was changed from "POLAR" to "IHEP".  And some line-wrapping was fixed.