A Simple Test of the External Shock Model for the Prompt Emission in Gamma-Ray Bursts

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, $n_{dec}$, and initial bulk Lorentz factor, ${\Gamma }_0$. This has the fortunate consequence of making the relation independent of both ${\Gamma }_0$ and $n_{dec}$. 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.

arXiv comment10 pages, 2 figures; submitted to ApJL

References in corpus (23)

• The collimation--corrected GRB energies correlate with the peak energy of their $\nu F_{\nu }$ spectrum
• Variability in GRBs - A Clue
• A 450-day light curve of the radio afterglow of GRB 970508: Fireball calorimetry
• Cosmological GRBs: Internal vs. External Shocks
• Pulse Width Evolution in GRBs: Evidence for Internal Shocks
• The efficiency of electron acceleration in collisionless shocks and GRB energetics
• Discovery of a tight correlation among the prompt emission properties of long Gamma Ray Bursts
• Prompt and Afterglow Emission Properties of Gamma-Ray Bursts with Spectroscopically Identified Supernovae
• Short Timescale Variability in the External Shock Model of Gamma Ray Bursts
• Radiation Front Sweeping the Ambient Medium of Gamma-Ray Bursts
• Accurate Calorimetry of GRB 030329
• Relativistic Winds from Compact Gamma-Ray Sources: II. Pair Loading and Radiative Acceleration in Gamma-ray Bursts
• Quiescent times in gamma-ray bursts: I. An observed correlation between the durations of subsequent emission episodes
• Electron-Positron Pair Cascades and Precursors in Gamma-Ray Bursts
• Precursors and electron-positron pair loading from erupting fireballs
• The Non-Relativistic Evolution of GRBs 980703 and 970508: Beaming-Independent Calorimetry
• Beam Models for Gamma-Ray Bursts Sources: Outflow Structure, Kinematics and Emission Mechanisms
• GRBs Light Curves - Another Clue on the Inner Engine
• Implications of the Measured Image Size for the Radio Afterglow of GRB 030329
• The apparent size of GRB afterglows as a test of the Fireball model
• Gamma-Ray Burst and Relativistic Shells: The Surface Filling Factor
• Prompt Gamma-ray and Early Afterglow Emission in the External Shock Model
• Creation of Electron--Positron Wind in Gamma-Ray Bursts and Its Effect on the Early Afterglow Emission

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