The structure of weakly magnetized γ-ray burst jets

Ore Gottlieb*, Omer Bromberg, Chandra B. Singh, Ehud Nakar

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

51 Scopus citations

Abstract

The interaction of gamma-ray burst (GRB) jets with the dense media into which they are launched promote the growth of local hydrodynamic instabilities along the jet boundary. In a companion paper, we study the evolution of hydrodynamic (unmagnetized) jets, finding that mixing of jet-cocoon material gives rise to an interface layer, termed jet-cocoon interface (JCI), which contains a significant fraction of the system energy. We find that the angular structure of the jet + JCI, when they reach the homologous phase, can be approximated by a flat core (the jet) + a power-law function (the JCI) with indices that depend on the degree of mixing. In this paper, we examine the effect of subdominant toroidal magnetic fields on the jet evolution and morphology. We find that weak fields can stabilize the jet against local instabilities. The suppression of the mixing diminishes the JCI and thus reshapes the jet's post-breakout structure. Nevertheless, the overall shape of the outflow can still be approximated by a flat core + a power-law function, although the JCI power-law decay is steeper. The effect of weak fields is more prominent in long GRB jets, where the mixing in hydrodynamic jets is stronger. In short GRB jets, there is small mixing in both weakly magnetized and unmagnetized jets. This result influences the expected jet emission which is governed by the jet's morphology. Therefore, prompt and afterglow observations in long GRBs may be used as probes for the magnetic nature at the base of the jets.

Original languageEnglish
Pages (from-to)3320-3333
Number of pages14
JournalMonthly Notices of the Royal Astronomical Society
Volume498
Issue number3
DOIs
StatePublished - 1 Nov 2020

Funding

FundersFunder number
Horizon 2020 Framework Programme818899

    Keywords

    • MHD
    • instabilities
    • methods: numerical

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