Constraints on cold magnetized shocks in gamma-ray bursts

Ramesh Narayan*, Pawan Kumar, Alexander Tchekhovskoy

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

We consider a model in which the ultrarelativistic jet in a gamma-ray burst (GRB) is cold and magnetically accelerated. We assume that the energy flux in the outflowing material is partially thermalized via internal shocks or a reverse shock, and we estimate the maximum amount of radiation that could be produced in such magnetized shocks. We compare this estimate with the available observational data on prompt γ-ray emission in GRBs. We find that, even with highly optimistic assumptions, the magnetized jet model is radiatively too inefficient to be consistent with observations. One way out is to assume that much of the magnetic energy in the post-shock, or even pre-shock, jet material is converted to particle thermal energy by some unspecified process, and then radiated. This can increase the radiative efficiency sufficiently to fit observations. Alternatively, jet acceleration may be driven by thermal pressure rather than magnetic fields. In this case, which corresponds to the traditional fireball model, sufficient prompt GRB emission could be produced either from shocks at a large radius or from the jet photosphere closer to the centre.

Original languageEnglish (US)
Pages (from-to)2193-2201
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Volume416
Issue number3
DOIs
StatePublished - Sep 2011

Keywords

  • Acceleration of particles
  • Gamma-ray burst: general
  • MHD
  • Radiation mechanisms: non-thermal
  • Relativistic processes
  • Shock waves

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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