A simple test of the external shock model for the prompt emission in gamma-ray bursts

Enrico Ramirez-Ruiz, Jonathan Granot

Research output: Contribution to journalArticlepeer-review

Abstract

It is demonstrated here that if the prompt GRB emission is produced by the simplest version of the external shock model, a specific relation should prevail between the observed duration, isotropic equivalent energy, and photon peak energy. In essence, this relation arises because both the burst duration and the typical energy of the emitted synchrotron photons depend on the same combination of the, usually poorly constrained, external density at the deceleration radius, ndec, and initial bulk Lorentz factor, Γ0. This has the fortunate consequence of making the relation independent of both Γ0 and ndec. Unless the efficiency of electron acceleration is very low, synchrotron gamma-rays from the external shock would fail to meet the current observational constraints for the vast majority of GRBs, including those with a smooth, single peak temporal profile. This argues either against an external shock origin for the prompt emission in GRBs or for changes in our understanding of the microphysical and radiation processes occurring within the shocked region.

Original languageEnglish
Pages (from-to)630-634
Number of pages5
JournalNew Astronomy
Volume12
Issue number8
DOIs
StatePublished - Nov 2007
Externally publishedYes

Bibliographical note

Funding Information:
We are especially grateful to Stan Woosley and Eli Waxman for discussions. We also thank the referee for highlighting the importance of SSC. This work is supported by IAS through a John Bahcall Fellowship award (ERR), by NASA through a Chandra Postdoctoral Fellowship award PF3-40028 (ERR) and by the Department of Energy under contract DE-AC03-76SF00515 (JG).

Keywords

  • Bursts - hydrodynamics - ISM
  • Gamma-rays
  • Jets and outflows

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