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The role of the magnetic fields in GRB outflows

Jordana-Mitjans, N, Mundell, CG, Kobayashi, S, Smith, RJ, Guidorzi, C, Steele, IA, Shrestha, M, Gomboc, A, Marongiu, M, Martone, R, Lipunov, V, Gorbovskoy, ES, Buckley, DAH, Rebolo, R and Budnev, NM (2023) The role of the magnetic fields in GRB outflows. In: Proceedings of the Sixteenth Marcel Grossmann Meeting. World Scientific Publishing Company, pp. 1449-1466. ISBN 9789811269769

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Gamma-ray bursts (GRBs) are bright extragalactic flashes of gamma-ray radiation and briefly the most energetic explosions in the Universe. Their catastrophic origin —the merger of compact objects or the collapse of massive stars— drives the formation of a newborn compact remnant (black hole or magnetar) that powers two highly relativistic jets. As these jets continue to travel outwards, they collide with the external material surrounding the dying star, producing a long-lasting afterglow that can be seen across the entire electromagnetic spectrum, from the most energetic gamma-ray emission to radio wavelengths. But how can such material be accelerated and focused into narrow beams? The internal shock model proposes that repeated collisions between material blasted out during the explosion can produce the gamma-ray flash. 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 directly probe the magnetic field properties in these extragalactic jets. This technology allowed the detection of highly polarized optical light in GRB 120308A and confirmed the presence of mildly magnetized jets with large-scale primordial magnetic fields in a reduced sample of GRBs (e.g. GRB 090102, GRB 110205A, GRB 101112A, GRB 160625B). Here we discuss the observations of the most energetic and first GRB detected at very high TeV energies, GRB 190114C, which opens a new frontier in GRB magnetic field studies suggesting that some jets can be launched highly magnetized and that the collapse and destruction of these magnetic fields at very early times may have powered the explosion itself. Additionally, our most recent polarimetric observations of the jet of GRB 141220A indicate that, when the jetted ejected material is decelerated by the surrounding environment, the magnetic field amplification mechanisms at the front shock —needed to generate the observed synchrotron emission— produce small magnetic domains. These measurements validate theoretical expectations and contrast with previous observations that suggest large magnetic domains in collisionless shocks (i.e. GRB 091208B)

Item Type: Book Section
Uncontrolled Keywords: astro-ph.HE; astro-ph.HE
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: World Scientific Publishing Company
Related URLs:
SWORD Depositor: A Symplectic
Date Deposited: 24 Jul 2023 14:45
Last Modified: 24 Jul 2023 14:45
DOI or ID number: 10.1142/9789811269776_0116
URI: https://researchonline.ljmu.ac.uk/id/eprint/20510
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