Hydrodynamic collimation of gamma-ray-burst fireballs

Area of Science:

• Astrophysics
• High-energy astrophysics
• Relativistic astrophysics

Background:

• Relativistic fireballs are key to understanding high-energy phenomena like gamma-ray bursts.
• The collimation mechanism of these fireballs is crucial for their observed properties.

Purpose of the Study:

• To derive analytic solutions for the hydrodynamic collimation of relativistic fireballs.
• To investigate the role of a surrounding baryonic wind from a torus in this collimation process.

Main Methods:

• Development of analytic solutions for relativistic hydrodynamic equations.
• Modeling the interaction between a central relativistic fireball and an external baryonic wind.

Main Results:

• The opening angle of the collimated jet is determined by the ratio of the fireball's power output to the baryonic wind's power output.
• Gamma-ray burst 990123 can be modeled as a baryon-poor jet (BPJ) with an energy output <= 10^50 erg.
• The collimating baryonic wind from a torus has an estimated energy output of ~10^52.5 erg.

Conclusions:

• The proposed model provides a framework for understanding jet collimation in astrophysical sources.
• The specific parameters derived for GRB 990123 suggest a significant energy contribution from the collimating wind.
• This work offers insights into the physics of relativistic outflows and their interaction with surrounding matter.