National Aeronautics and Space Administration

The POLAR instrument was a gamma-ray burst polarimeter on China’s Tiangong 2 space lab. While the highlight of Tiangong 2 was the manned flight mission to the space station, a number of instruments worked over a three year span working autonomously, including POLAR. The space station was deliberately de-orbited in a controlled re-entry in July 2019. The instrument had recoreded some 55 bursts and obtained high-precision polarization measurements for five of these burst events.

POLAR should not be confused with GGS Polar, a near-Earth space environment study satellite which operated between 1996 and 2008.

POLAR consisted of a 40 x 40 array of plastic scintillator bars, with a total effective area of 400 cm². These are protected by passive shielding outside the wide field of view of the instrument which covered roughly one third of the sky. It used the Compton scattering effect to measure polarization of incoming photons.

POLAR observed 55 gamma-ray bursts during the mission, including five bursts for which detailed polarization measurements were available