POLAR: The first detailed polarization measurements of the brightest explosions in the Universe

17.04.2019 11:15 – 12:15

Gamma-Ray Bursts (GRBs) are the most violent explosions in the Universe since the Big Bang. These events, which despite occurring millions or even billions of light years away, are observed approximately once per day. Some are thought to be the result of the death of very massive stars while, thanks to gravitational wave measurements, a subset was recently shown to be the result of the merging of 2 neutron stars. The extreme brightness of these events allowed them to be discovered by accident more than 50 years ago by some of the first gamma-ray detectors operating in space. While since then great progress was made in our understanding of these events through studies of the arrival time, direction and energy of the gamma-rays emitted in these explosions, many open questions remain and appear difficult or even impossible to be answered using conventional studies. In recent decades theoretical studies have indicated that a wealth of information is contained in the one remaining unmeasured parameter of these photons: their polarization.

The POLAR instrument was designed specifically to provide the first detailed polarization measurements of GRBs. POLAR was developed by a collaboration of institutes in Switzerland, Poland and China, and launched in September 2016 as part of the second Chinese space lab, the Tiangong-2. It took data for a total of 6 months during which it detected a total of 55 GRBs as well as several other astrophysical objects. The complicated polarization analysis of 5 of these GRBs was recently completed. The results indicate that the polarization is more complicated than any of the existing models suggest. During this talk I will provide an introduction to GRB astrophysics, discus the history of the POLAR mission and present the first results of this mission and their interpretation (or at least explain the lack thereof).

Lieu

Bâtiment: Ecole de Physique

Quai Ernest-Ansermet 24
1211 Genève 4
Grand Auditoire A

entrée libre