Please enable JavaScript.
Coggle requires JavaScript to display documents.
Lecture 4- Synchrotron emission (Beamed emission (In electrons rest frame,…
Lecture 4- Synchrotron emission
General
Radio galaxies - Double radio structure (Cygnus A)
Steeply falling spectra, fainter when observed at higher radio frequencies
produced by highly energetic electrons, travelling near speed of light and interacting with magnetic fields
Linearly polarised
non thermal brightness temperature
Lorentz force
force provided by magnetic field
Electrons moving at reletivistic speeds, so consider the lorentz force in the rest frame of the electron
MAATHS
Energy loss
Lorentz invariant quality, so observer will see same energy loss as the electron sees in its own rest frame
Need to average over all pitch angles
Beamed emission
In electrons rest frame, the emission has a dipole shape
dipole is distorted in the observers frame
the side of the dipole in the direction of motion is boosted because of reletivistic motion
this changes the distribution of the emission
The faster the electron is moving, the larger gamma becomes and the narrower the beam of emission becomes
Observer see emission as super fast pulses emitted every time the electron circles the magnetic field and its velocity is towards the observer
Flashes of emission
length of flashes can be calculated by considering the difference in arrival time between emission at start of pulse and end of pulse
Diagram
Emission from point A needs to travel a distance s further to reach the observer than emission from point B
takes s/c longer
But emission from point B will be produced later by a time s/v
Maths
Energy Distribution
Peak frequency depends on the energy of the electron
average over the distribution of electron energies
Ultra-relativistic electrons follow a power-law distribution
known as Non-thermal distribution
maths, p depends on the mechanism that accelerates the elctrons up to such high energies
Emissivity of syncrotron plasma
Should observe synchrotron emission which dims steeply with frequency, with a power law index