The POLAR gamma-ray burst polarimeter onboard the Chinese Spacelab

Abstract

POLAR is a joint European-Chinese experiment aimed at a precise measurement of hard X-ray polarization (50−500 keV) of the prompt emission of Gamma-Ray Bursts. The main aim is a better understanding of the geometry of astrophysical sources and of the X-ray emission mechanisms. POLAR is a compact Compton polarimeter characterized by a large modulation factor, effective area, and field of view. It consists of 1600 low-Z plastic scintillator bars read out by 25 flat-panel multi-anode photomultipliers. The incoming X-rays undergo Compton scattering in the bars and produce a modulation pattern; experiments with polarized synchrotron radiation and GEANT4 Monte Carlo simulations have shown that the polarization degree and angle can be retrieved from this pattern with the accuracy necessary for identifying the GRB mechanism. The flight model of POLAR is currently under construction in Geneva. The POLAR instrument will be placed onboard the Chinese spacelab TG-2, scheduled for launch in low Earth orbit in 2015. The main milestones of the space qualification campaign will be described in the paper.

Polarimetric Analysis of the Long Duration Gamma-Ray Burst GRB 160530A With the Balloon Borne Compton Spectrometer and Imager

“…One exception is IKAROS/GAP (Yonetoku et al 2011a), a dedicated GRB polarimeter aboard the JAXA solar sail IKAROS which is responsible for the most significant GRB polarization measurements to date (Yonetoku et al 2012). The POLAR instrument aboard the Chinese space station Tiangong 2 is another dedicated GRB polarimeter which was only recently deployed (Sun et al 2016;Orsi et al 2014;Produit et al 2005). POLAR has successfully detected several GRBs in its few months of service (Kole & Marcinkowski 2016;, although no polarization analyses have yet been published.…”