Accepted for publication in Reviews of Modern Physics
astro-ph/0405503

For a PDF version of the article, click here.


THE PHYSICS OF GAMMA-RAY BURSTS

Tsvi Piran *


Racah Institute for Physics, The Hebrew University, Jerusalem, 91904, Israel
tsvi@phys.huji.ac.il


Abstract. Gamma-Ray Bursts (GRBs), short and intense pulses of low energy gamma-rays, have fascinated astronomers and astrophysicists since their unexpected discovery in the late sixties. During the last decade, several space missions: BATSE (Burst and Transient Source Experiment) on Compton Gamma-Ray Observatory, BeppoSAX and now HETE II (High-Energy Transient Explorer), together with ground optical, infrared and radio observatories have revolutionized our understanding of GRBs showing that they are cosmological, that they are accompanied by long lasting afterglows and that they are associated with core collapse Supernovae. At the same time a theoretical understanding has emerged in the form of the fireball internal-external shocks model. According to this model GRBs are produced when the kinetic energy of an ultra-relativistic flow is dissipated in internal collisions. The afterglow arises when the flow is slowed down by shocks with the surrounding circum-burst matter. This model has numerous successful predictions like the prediction of the afterglow itself, the prediction of jet breaks in the afterglow light curve and of an optical flash that accompanies the GRBs themselves. In this review I focus on theoretical aspects and on physical processes believed to take place in GRBs.


Table of Contents

INTRODUCTION

OBSERVATIONS
Prompt Emission
The Afterglow
Hosts and Distribution
Energetics

THE GLOBAL PICTURE - GENERALLY ACCEPTED INGREDIENTS

RELATIVISTIC EFFECTS
Compactness and relativistic motion
Relativistic time effects
Relativistic Beaming and the Patchy Shell Model

PHYSICAL PROCESSES
Relativistic Shocks
Particle Acceleration
Synchrotron
Inverse Compton
Quasi-Thermal Comptonization
Polarization from Relativistically Moving Sources

THE GRB AND THE PROMPT EMISSION
Internal vs. External Shocks
Internal Shocks
External Shocks
The Transition from Internal Shocks to External Shocks
Prompt Polarization

THE AFTERGLOW
Relativistic Blast Waves and the Blandford-McKee solution
Light Curves for the "Standard" Adiabatic Synchrotron Model
Light Curves for the early radiative phase
Light Curve During the Newtonian transition
Generalizations: I. Winds
Generalizations: II. Energy injection and refreshed shocks
Generalizations: III. Inhomogeneous density profiles
Generalizations: IV. Jets
Generalizations: V. Angular Dependent Jets and the Structured Jet Model
Afterglow Polarization - a tool that distinguished between the different jet models
Orphan Afterglows
Generalizations: VI. Additional Physical Processes

ADDITIONAL EMISSION FROM GRBs
TeV gamma-rays
Neutrinos
Cosmic Rays and Ultra High Energy Cosmic Rays
Gravitational Radiation

MODELS OF INNER ENGINES
Black hole accretion
The Pulsar Model
Rotating black holes and the Blandford Znajek mechanism
The Collapsar Model
The Supranova Model
Merging neutron stars

OPEN QUESTIONS AND FUTURE PROSPECTS

REFERENCES



* Electronic address: tsvi@phys.huji.ac.il

Next