A "Boosted Fireball" Model for Structured Relativistic Jets
Abstract
We present a model for relativistic jets which generates a particular angular distribution of Lorentz factor and energy per solid angle. We consider a fireball with specific internal energy E/M launched with bulk Lorentz factor γ B . In its center-of-momentum frame the fireball expands isotropically, converting its internal energy into radially expanding flow with asymptotic Lorentz factor η0 ~ E/M. In the lab frame the flow is beamed, expanding with Lorentz factor Γ = 2η0γ B in the direction of its initial bulk motion and with characteristic opening angle θ0 ~ 1/γ B . The flow is jet-like with Γθ0 ~ 2η0 such that jets with Γ > 1/θ0 are naturally produced. The choice η0 ~ γ B ~ 10 yields a jet with Γ ~ 200 on-axis and angular structure characterized by opening angle θ0 ~ 0.1 of relevance for cosmological gamma-ray bursts (GRBs), while γ B >~ 1 may be relevant for low-luminosity GRBs. The model produces a family of outflows, of relevance for different relativistic phenomena with structures completely determined by η0 and γ B . We calculate the energy per unit solid angle for the model and use it to compute light curves for comparison with the widely used top-hat model. The jet break in the boosted fireball light curve is greatly subdued when compared to the top-hat model because the edge of the jet is smoother than for a top-hat. This may explain missing jet breaks in afterglow light curves.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2013
- DOI:
- 10.1088/2041-8205/776/1/L9
- arXiv:
- arXiv:1308.1731
- Bibcode:
- 2013ApJ...776L...9D
- Keywords:
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- gamma-ray burst: general;
- hydrodynamics;
- relativistic processes;
- shock waves;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- ApJ Accepted