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VegasAfterglow: An Advanced Toolkit for Modeling GRB Afterglows

Yihan Wang, Connery Chen & Bing Zhang

Nevada Center for Astrophysics, UNLV

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We developed a code

mainly for GRB afterglow

It supports:

-Arbitrary non-axisymmetric energy/Gamma/magnetization profiles

-Forward, Reverse shock and jet spreading

-Relativistic & Non-relativistic regimes

-Self-absorption

-Arbitrary energy injection

-Inverse compton process with Klein-Nishina correction

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Apple M4 single core w/ clang 16.0.0

It’s ~50x faster than available good public GRB afterglow code

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Jet

-energy profile

-Lorentz factor profile

-magnetization profile

-injection function

-spreading

Medium

-density profile

-microphysics parameters

 

Forward shock

-bulk Lorentz factor

-comoving B field

-down str # density

-shock width

…

Reverse shock

-bulk Lorentz factor

-comoving B field

-down str # density

-shock width

…

 

 

 

 

 

 

 

 

 

 

Observer

-viewing angle

-luminosity distance

-observing frequencies

Observations

-flux

-spectrum

…

Dynamics

Radiation

Geometry

GRB Afterglow

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Urrutia + 2022

 

medium

 

 

jet

 

 

 

 

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Chiang&Dermer 1999; Piran 1999;

Shock Dynamics

 

 

Zhang 2018

Huang et al. 1999, 2000

 

 

+ radiation

 

 

Pe’er 2012

Nava et al. 2013

+ pressure

+ adiabatic expansion

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Shock Dynamics - Tophat Jet

 

coasting

deceleration

Newtonian

coasting

deceleration

Newtonian

 

 

 

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Shock Dynamics – structured Jet

 

 

Gaussian Jet

Powerlaw Jet

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Shock Dynamics – Energy injection

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Shock Dynamics – Energy injection

 

acceleration

deceleration

Newtonian

acceleration

deceleration

Newtonian

injection ends

Gaussian Jet + spin down

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Shock Dynamics – user defined Jet

Energy profile

 

Injection function

 

Initial Lorentz factor profile

 

Initial magnetization profile

 

All can be customized!

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Shock Dynamics – user defined Jet

A random example

synchrotron X-ray emission

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Shock Dynamics – Reverse shock

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Shock Dynamics – Reverse shock

I

(unshocked medium)

II

(shocked medium)

III

(shocked ejecta)

IV

(unshocked ejecta)

DC

forward shock front

reverse shock front

 

 

 

 

Zhang&Kobayashi 2005

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Shock Dynamics – Jet spreading

 

 

Tophat jet in ISM

jet break

Newtonian

 

 

 

 

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Radiation: Synchrotron spectrum

mapping

 

 

 

 

 

 

 

 

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Radiation: Synchrotron spectrum

mapping

 

 

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slow cooling, weak absorption

slow cooling, medium absorption

fast cooling, weak absorption

fast cooling, medium absorption

strong absorption

Radiation: Synchrotron spectrum

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Radiation: Synchrotron spectrum

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LHAASO 2023

Radiation: Inverse Compton

MAGIC 2019

190114C

221009A

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Radiation: Inverse Compton

Shock front

Up stream

Down stream

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Radiation: Inverse Compton

electron distribution

photon spectrum

 

 

 

 

 

 

 

 

?

IC cooling

?

IC spectrum

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Gao, Lei, Wu & Zhang 2013

 

electron distribution

photon spectrum

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Radiation: Inverse Compton

electron distribution

photon spectrum

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Radiation: Inverse Compton

electron distribution

IC spectrum

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Radiation: Inverse Compton

Optical

RS electron

FS electron

RS photon

FS photon

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Jet

-energy profile

-Lorentz factor profile

-magnetization profile

-injection function

-spreading

Medium

-density profile

-microphysics parameters

 

Forward shock

-bulk Lorentz factor

-comoving B field

-down str # density

-shock width

…

Reverse shock

-bulk Lorentz factor

-comoving B field

-down str # density

-shock width

…

 

 

 

 

 

 

 

 

 

 

Observer

-viewing angle

-luminosity distance

-observing frequencies

Observations

-flux

-spectrum

…

GRB Afterglow

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Model level optimization

Algorithm/code level optimization

Black Magic

Apple M4 single core w/ clang 16.0.0

 

Gaussian jet/ISM

Synchrotron only

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Zoom out

Model level optimization

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Model level optimization

 

 

 

Grids that perform real calculations

interpolations

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Off-axis Gaussian jet

Model level optimization

Converged grid size:

128x128x128 (without interpolations)

​

​

​

32x32x32 (with interpolations)

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Algorithm level optimization

Ingredients (data)

Recipe (algorithm)

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Algorithm level optimization

Data scale

# of operations

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In seconds

In minutes

CPU

~ bytes

Cache

~ MB

RAM

~ GB

Algorithm level optimization

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Black Magic

shock ODE

spectrum evaluation/interpolation

others

log

exp

pow

relative precision ~10-16

total CPU cost

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Black Magic

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Radiation: deep Newtonian regime in GW170817

 

LOS

tobs=1000 d

The shock dynamics of GW170817 after 1000 days is already in the deep Newtonian regime

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Radiation: deep Newtonian regime in GW170817

 

 

 

cyclotron

synchrotron

 

 

 

 

 

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pitch angle

viewing angle

First kind Bessel function

 

 

 

 

 

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transition from synchrotron to cyclotron

 

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Radiation: cyclotron cutoffs on GW170817

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We developed a code

We call it VegasAfterglow

It supports:

-Arbitrary non-axisymmetric energy/Gamma/magnetization profiles

-Forward, Reverse shock and jet spreading

-Relativistic & Non-relativistic regimes

-Self-absorption

-Arbitrary energy injection

-Inverse compton with Klein-Nishina correction

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Apple M4 single core w/ clang 16.0.0

It’s ~50x faster than available good public GRB afterglow code

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Light curves in X-ray band

…

Fiducial GW170817

Narrower jet

Wider jet

Smaller viewing angle

Larger viewing angle