[vsnet-grb-info 18678] GRB 160928A: The first GRB detected by POLAR

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20126
SUBJECT: GRB 160928A: The first GRB detected by POLAR
DATE:    16/11/04 15:30:06 GMT
FROM:    Shaolin Xiong at POLAR  <xiongsl at ihep.ac.cn>

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/.