Gamma-ray Bursts (GRBs) are the most powerful explosions in the Universe. When a massive star in a distant galaxy collapses into a black hole, the material is accelerated to ultra-high speeds along the narrow beam of a jet. As this jet continues to travel outwards, it collides with external material surrounding the dying star, producing fading light called the “afterglow” that can be seen across the entire electromagnetic spectrum, from the most energetic gamma-rays to radio wavelengths.
But how can such material be accelerated and focused into narrow beams? The internal shock model proposes that repeated violent collisions between material blasted out during the explosion can produce the gamma-ray flash and the subsequent fading afterglow. The competing magnetic model credits primordial large-scale ordered magnetic fields that collimate and accelerate the relativistic outflows. To distinguish between these models and ultimately determine the power source for these energetic explosions, our team studies the polarization of the light during the first minutes after the explosion (using novel instruments on fully autonomous telescopes around the globe) to probe directly the magnetic field properties in these distant jets.
Using this technology, our team made the first detection of highly polarized optical light and confirmed the presence of mildly magnetized jets with large-scale primordial magnetic fields (e.g., GRB 120308A; Mundell et al. 2013). Our most recent observations of the most energetic and first GRB detected at very high TeV energies (GRB 190114C) opens a new frontier in GRB magnetic field studies suggesting that some jets can be launched highly magnetized (Jordana-Mitjans et al. 2020) and that the collapse and destruction of these fields at very early times may have powered the explosion itself.