Magnetohydrodynamic simulations of gamma-ray burst jets: Beyond the progenitor star

Alexander Tchekhovskoy*, Ramesh Narayan, Jonathan C. McKinney

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

107 Scopus citations


Achromatic breaks in afterglow light curves of gamma-ray bursts (GRBs) arise naturally if the product of the jet's Lorentz factor γ and opening angle Θj satisfies γΘj≫1 at the onset of the afterglow phase, i.e., soon after the conclusion of the prompt emission. Magnetohydrodynamic (MHD) simulations of collimated GRB jets generally give γΘj≲1, suggesting that MHD models may be inconsistent with jet breaks. We work within the collapsar paradigm and use axisymmetric relativistic MHD simulations to explore the effect of a finite stellar envelope on the structure of the jet. Our idealized models treat the jet-envelope interface as a collimating rigid wall, which opens up outside the star to mimic loss of collimation. We find that the onset of deconfinement causes a burst of acceleration accompanied by a slight increase in the opening angle. In our fiducial model with a stellar radius equal to 104.5 times that of the central compact object, the jet achieves an asymptotic Lorentz factor γ∼500 far outside the star and an asymptotic opening angle Θj≃0. 04rad≃2°, giving γΘj∼20. These values are consistent with observations of typical long-duration GRBs, and explain the occurrence of jet breaks. We provide approximate analytic solutions that describe the numerical results well.

Original languageEnglish (US)
Pages (from-to)749-754
Number of pages6
JournalNew Astronomy
Issue number8
StatePublished - Nov 2010


  • Accretion
  • Accretion disks
  • Black hole physics
  • Galaxies: jets
  • Gamma rays: bursts
  • MHD
  • Relativity

ASJC Scopus subject areas

  • Instrumentation
  • Astronomy and Astrophysics
  • Space and Planetary Science


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