Published in Phys.Rept. 314 (1999) 575-667.

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GAMMA-RAY BURSTS AND THE FIREBALL MODEL

Tsvi Piran


Racah Institute for Physics, The Hebrew University, Jerusalem, 91904, Israel 1
and
Physics Department, Columbia University, New York, NY 10027, USA


Abstract. Gamma-ray bursts (GRBs) have puzzled astronomers since their accidental discovery in the late sixties. The BATSE detector on the COMPTON-GRO satellite has been detecting one burst per day for the last six years. Its findings have revolutionized our ideas about the nature of these objects. They have shown that GRBs are at cosmological distances. This idea was accepted with difficulties at first. The recent discovery of an X-ray afterglow by the Italian/Dutch satellite BeppoSAX has led to a detection of high red-shift absorption lines in the optical afterglow of GRB970508 and in several other bursts and to the identification of host galaxies to others. This has confirmed the cosmological origin. Cosmological GRBs release ~ 1051 - 1053 ergs in a few seconds making them the most (electromagnetically) luminous objects in the Universe. The simplest, most conventional, and practically inevitable, interpretation of these observations is that GRBs result from the conversion of the kinetic energy of ultra-relativistic particles or possibly the electromagnetic energy of a Poynting flux to radiation in an optically thin region. This generic "fireball" model has also been confirmed by the afterglow observations. The "inner engine" that accelerates the relativistic flow is hidden from direct observations. Consequently it is difficult to infer its structure directly from current observations. Recent studies show, however, that this "inner engine" is responsible for the complicated temporal structure observed in GRBs. This temporal structure and energy considerations indicates that the "inner engine" is associated with the formation of a compact object - most likely a black hole.


Table of Contents

INTRODUCTION

OBSERVATIONS
Duration
Temporal Structure and Variability
Spectrum
Spectral Evolution
Spectral Lines
Angular Positions
Angular Distribution
Quiescent Counterparts and the historical "No Host" Problem
Afterglow
Repetition?
Correlations with Abell Clusters, Quasars and Supernovae
V/Vmax, Count and Peak Flux Distributions

THE DISTANCE SCALE
Redshift Measurements.
The Angular Distribution
Interpretation of the Peak Flux Distribution
Time Dilation

THE COMPACTNESS PROBLEM AND RELATIVISTIC MOTION
Relativistic Motion
Relativistic Beaming?

AN OVERVIEW OF THE GENERIC MODEL
Models for The Energy Flow
Models for The Energy Conversion
Typical Radii

FIREBALLS
A simple model
Extreme-Relativistic Scaling Laws.
The Radiation-Dominated Phase
The Matter-Dominated Phase
Spreading
Optical Depth
Anisotropic Fireballs

TEMPORAL STRUCTURE AND KINEMATIC CONSIDERATIONS
Time-scales
Angular Spreading and External shocks
Angular Variability and Other Caveats
Temporal Structure in Internal shocks.

ENERGY CONVERSION
Slowing Down of Relativistic Particles
Synchrotron Emission from Relativistic Shocks
Synchrotron Self Absorption
Inverse Compton Emission
Radiative Efficiency
Internal Shocks
Shocks with the ISM - External shocks
The Internal - External Scenario

AFTERGLOW
Hydrodynamics of a Slowing Down Relativistic Shell
Phases in a Relativistic Decelerating Shell
Synchrotron Emission from a Relativistic Decelerating Shell
New Puzzles from Afterglow observations

MODELS OF THE INNER ENGINE
The "Inner Engine"
NS2Ms: Binary Neutron Star Mergers
Binary Neutron Stars vs. Black Hole - Neutron star Mergers

OTHER RELATED PHENOMENA
Cosmic Rays
UCHERs - Ultra High Energy Cosmic Rays
High Energy Neutrinos
Gravitational Waves
Low Energy Neutrinos
Black Holes

COSMOLOGICAL IMPLICATIONS

SUMMARY AND CONCLUSIONS

REFERENCES



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