1. Afterglow Radiation from Gamma-Ray Bursts
Hugh Desmond
Katholieke Universiteit Leuven
Weiqun Zhang
SLAC

2. Outline
Background
The project
Results and discussion

3. GRBs GRB: Brightest known source of gamma rays
The afterglow: a residual radiation in lower frequencies
GRBs occur at cosmological distances

4. GRB Model Collapse of massive star leads to accretion disk.
A jet is shot off along rotation axis.
Electrons in the ISM are accelerated to relativistic speeds.
The magnetic field in the jet causes the electrons to emit synchrotron radiation, the afterglow.

5. Previous studies Calculated the afterglow based on an analytical model
This model simplified the jet’s sidewards expansion

6. The hydrodynamical simulation

7. The hydrodynamical simulation
It gave the necessary data:
internal energy,
bulk velocity,
particle density,

8. The project: methods Micro-physics of the jet is unknown; assumption:
This allowed and to be determined through

9. The project: methods
Further assumption: the electron energy within the jet follows a power-law distribution.

10. The project: methods
From these assumptions, the power per unit volume per unit frequency can be calculated:
To transform into observer frame, we take into account
Redshift
Doppler shift
Transit time

11. Results: lightcurve
Flux follows broken power-law:

12. Results: lightcurve Two potential explanations for decay after break:
Sidewards expansion leads to a faster drop in energy density
The edge of the jet is seen
Counter-jet

13. Results: spectrum
The spectrum agrees with previous studies

14. Conclusion Numerical simulation + assumptions:
electron energy and magnetic field energy fixed fraction of total
Electron energy follows distribution
We found that the lightcurves differ from those of the analytical model.
Future work:
Moving observer off the rotation axis
Calculating the image
Change initial density and energy of the jet to a non-uniform distribution