collisionless shocks in gamma ray bursts current results and future perspectives
DESCRIPTION
Collisionless shocks in Gamma Ray Bursts Current results and future perspectives. Århus, September 2005. Troels Haugbølle. [email protected]. Collaborators: Jacob Trier Frederiksen, Christian Hededal, Åke Nordlund. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/1.jpg)
Collisionless shocks in Gamma Ray BurstsCurrent results and future perspectives.
Århus, September 2005
Troels Haugbø[email protected]
Dark Cosmology Centre, Niels Bohr Institute
Collaborators: Jacob Trier Frederiksen, Christian Hededal, Åke Nordlund
![Page 2: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/2.jpg)
Contents
● Gamma Ray Bursts as extreme physics laboratories
●Simulation tool: A Particle-In-Cell code●Collisionless Shocks
● Current results:●Magnetic field generation●Particle Acceleration
● A Next Generation Particle-In-Cell code:●Design and preliminary results
![Page 3: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/3.jpg)
The GRB Fireball Model
(Aloy et 99)
![Page 4: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/4.jpg)
The GRB Fireball Model
Mean Free Path >> Shock extent => A collisionless shock
(Aloy et 99)
Low Density
High Density
>> 1
Low Density
>> 1
High Density
![Page 5: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/5.jpg)
A collisionless =15 shock
QuickTime™ and aBMP decompressor
are needed to see this picture.
![Page 6: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/6.jpg)
Collisionless shocks
● Collisionless shocks are abundant in the universe.They are found in:
● Gamma Ray Burst afterglows
● Internal shocks in AGNs
● Supernova remnants
● Shocks in the large scale structure
![Page 7: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/7.jpg)
Collisionless shocks● The fluid picture, used
as the basis for large scale models, must be abandoned
● Collisions are mediated through the macroscopic electro magnetic field
● Charge separation occurs
● There is no local equilibrium
● We need to understand the physics on a more fundamental level!
![Page 8: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/8.jpg)
Simulation tool:Relativistic Particle-in-cell code
Fields on mesh
Sampledparticles
● The code solves Maxwell's equations together with the Lorentz force on the particles
![Page 9: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/9.jpg)
Magnetic Field Generation in Gamma Ray Burst Afterglows● Strong synchrotron like radiation is observed from Gamma Ray
Burst Afterglows● Two main components are needed to explain the radiation
● A strong magnetic field
● A powerlaw distributed population of electrons
● Obvious candidates for explaining the magnetic field fails:● The magnetic field of the interstellar medium
compressed in front of the shock is too weak by afactor of at least 1000
● The magnetic field generated by the central engine carried along with the plasma is too weak
![Page 10: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/10.jpg)
Magnetic field generationThe Weibel instability
● An alternative explanation:
The magnetic field is generated in situ
● Two counter streaming collisionless plasma are susceptible to the Weibel instability
● In our simulations we are at rest in the outflow from the Gamma ray burst
(Here inflow =3, density jump=3)
![Page 11: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/11.jpg)
The Weibel instability
The linear phase
The non linear phase
![Page 12: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/12.jpg)
The Weibel instability
The linear phase
The non linear phase
![Page 13: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/13.jpg)
The Weibel instability
The linear phase
The non linear phase
![Page 14: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/14.jpg)
The Weibel instability for a two component plasma
![Page 15: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/15.jpg)
The Weibel instability for a two component plasma
QuickTime™ and aCinepak decompressor
are needed to see this picture.
![Page 16: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/16.jpg)
First result: Magnetic field generation
● The magnetic field generated by the Weibel instability is● Containing up to 5% of equipartition● At least 1000 times stronger than
the shock compressed ISM field● Selfsimilar: The Fourier trans-form
of the field is a powerlaw● Is highly turbulent: B/B ~ 1● Transverse to the flow B∥/B⊥~ 0.1● Not possible to parameterize simply
with B (Frederiksen et al., 2002, 2004)
![Page 17: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/17.jpg)
Second ingredient: Particle Acceleration● Strong synchrotron like radiation is observed from
Gamma Ray Burst Afterglows● Two main components are needed to explain the
radiation
●A strong magnetic field
●A powerlaw distributed population of high energy electrons
● The acceleration of the electrons is normally explained by invoking Fermi acceleration
● From test particle simulations it has been shown that the power law index for the electrons should universally be p=2.2
● Observations of GRB afterglows points to no universal p
![Page 18: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/18.jpg)
Second ingredient: Particle Acceleration● Strong synchrotron like radiation is observed from
Gamma Ray Burst Afterglows● Two main components are needed to explain the
radiation
●A strong magnetic field
●A powerlaw distributed population of high energy electrons
● Fermi acceleration works by scattering particles across the shock in a recursive process
● If the “Weibel picture” is correct, themagnetic field is much weaker outsidethe shock front. How can the electronsbe backscattered then?
![Page 19: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/19.jpg)
Potential acceleration of the electrons:
Electrons inside the Debye sphere are accelerated because of the ion Weibel instability.
(Hededal et al., 2004)
`
![Page 20: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/20.jpg)
A Non-Fermi Power law acceleration scenario
Pow
er
Wavenumber JIon
v
v
d
N/d
log
(v)
![Page 21: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/21.jpg)
Conclusions
● We have demonstrated the importance of the Weibel instability in understanding collisionless shocks● It creates a highly tangled, transverse magnetic field
containing up to 5% of equipartition energy● In electron-ion dominated plasmas electrons can be
accelerated/heated and a non-thermal tail is formed
● It is not possible to consider B,
e and p as separate
parameters, but rather a product of the same process physical process
![Page 22: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/22.jpg)
The project has been successful so far...but the code is limited
● No radiative transfer
● No collisions
● No photon-plasma or other general particle interactions
● Only radiative (synchrotron) cooling
![Page 23: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/23.jpg)
Challenges ahead – what we would like to model ● Collisionless shocks are prevalent; but still there are
interesting scenarios with collisions/ interactions playing an important role: ● Black hole coronas and inner jets ● The solar corona/space weathering
● Internal shocks in GRBs
● Pre-acceleration in Supernovae remnants for CR
![Page 24: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/24.jpg)
Our answer: A next generation PIC code● Characteristics to keep in mind:
● Radiative cooling ● General scattering processes using discrete
methods
● Annihilation/pair creation; neutron decay
● A kinetic particle description with the EM-
fields on a mesh – but with general particles
![Page 25: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/25.jpg)
First test of Compton interactionsA laser beam shining on a thin pair plasma
● To compare directly with theory we
● Fixed a pair plasma with T~0K● Injected a laser beam with E=10m
ec2
![Page 26: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/26.jpg)
First test of Compton interactionsA laser beam shining on a thin pair plasma
QuickTime™ and aCinepak decompressor
are needed to see this picture.
![Page 27: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/27.jpg)
Differential cross section
![Page 28: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/28.jpg)
Future outlook:
● Internal shocks in GRBs is a prime target● But many other interesting things to do – photon
transport makes it easier to compare with observations● The code in itself is the perfect infrastructure for
general particle/field simulations with general _microphysical_ interactions
![Page 29: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/29.jpg)
For the dessert: Eye candy!
![Page 30: Collisionless shocks in Gamma Ray Bursts Current results and future perspectives](https://reader036.vdocument.in/reader036/viewer/2022062802/568144ba550346895db1833e/html5/thumbnails/30.jpg)
QuickTime™ and aCinepak decompressor
are needed to see this picture.