Book contents
- Frontmatter
- Contents
- List of contributors
- Prologue
- 1 The discovery of the gamma-ray burst phenomenon
- 2 Instrumental principles
- 3 The BATSE era
- 4 The cosmological era
- 5 The Swift era
- 6 Discoveries enabled by multiwavelength afterglow observations of gamma-ray bursts
- 7 Prompt emission from gamma-ray bursts
- 8 Basic gamma-ray burst afterglows
- 9 The GRB–supernova connection
- 10 Models for gamma-ray burst progenitors and central engines
- 11 Jets and gamma-ray burst unification schemes
- 12 High-energy cosmic rays and neutrinos
- 13 Long gamma-ray burst host galaxies and their environments
- 14 Gamma-ray burst cosmology
- 15 Epilogue
- Indix
- Plate section
- References
11 - Jets and gamma-ray burst unification schemes
Published online by Cambridge University Press: 05 December 2012
- Frontmatter
- Contents
- List of contributors
- Prologue
- 1 The discovery of the gamma-ray burst phenomenon
- 2 Instrumental principles
- 3 The BATSE era
- 4 The cosmological era
- 5 The Swift era
- 6 Discoveries enabled by multiwavelength afterglow observations of gamma-ray bursts
- 7 Prompt emission from gamma-ray bursts
- 8 Basic gamma-ray burst afterglows
- 9 The GRB–supernova connection
- 10 Models for gamma-ray burst progenitors and central engines
- 11 Jets and gamma-ray burst unification schemes
- 12 High-energy cosmic rays and neutrinos
- 13 Long gamma-ray burst host galaxies and their environments
- 14 Gamma-ray burst cosmology
- 15 Epilogue
- Indix
- Plate section
- References
Summary
Evidence for bulk relativistic motion in gamma-ray bursts
The first line of evidence for ultrarelativistic bulk motion of the outflows that produce GRBs arises from the compactness argument. It relies on the observed short and intense pulses of gamma rays and their non-thermal energy spectrum that often extends up to high photon energies. Together, these facts imply that the emitting region must be moving relativistically. In order to understand this better, let us first consider a source that is either at rest or moves at a Newtonian velocity, β≡ v/c ≪1, corresponding to a bulk Lorentz factor Γ (1 – β2)−1/2 ≈ 1. For such a source the observed variability timescale (e.g., the width of the observed pulses) ∆t, implies a typical source size or radius R <c∆t, due to light time travel effects (for simplicity we ignore here cosmological effects, such as redshift or time of dilation). GRBs often show significant variability down to millisecond timescales, implying R<3 × 107(∆t/ 1 ms) cm. At cosmological distances their isotropic equivalent luminosity, L, is typically in the range of 1050–1053 erg s−1. In addition, the (observed part of the) εFε GRB spectrum typically peaks around a dimensionless photon energy of ε≡ Eph/mec2 ˜ 1, so that (for a Newtonian source) a good fraction of the total radiated energy is carried by photons that can pair produce with other photons of similar energy. (F is the radiative flux and Fε ≡ dF/dε.)
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- Gamma-ray Bursts , pp. 215 - 250Publisher: Cambridge University PressPrint publication year: 2012
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