Synchrotron emission from supernovas by charged particles in a non-uniform magnetic field
Our universe contains many mysteries that humans haven’t solved yet. Every time we get a
little closer to understanding our universe little bit better than before, our universe throws more
questions and mysteries at us for us to solve. One of such mysteries is cosmic rays.
Cosmic rays are very high energy radiation which mainly originates from outside our solar system or even milky way galaxy. The range of energies encompassed by cosmic rays is truly enormous, starting at about 10 7 eV and reaching 10 20 eV for the most energetic cosmic ray ever detected. We still don’t understand everything about these cosmic rays.
One of the ways by which we characterise and study properties of cosmic rays is with the help of the so-called cosmic ray spectrum. When we plot the range of energies against the number of cosmic rays detected at each energy(Flux) we generate a cosmic ray spectrum.
The number of cosmic rays drops off dramatically as we go to higher energies. The origin of these changes in the steepness of the spectrum is still the subject of intense study, but it is assumed that they distinguish between populations of cosmic rays originating via different mechanisms.
Study of cosmic rays has been a challenging tasks for scientists for decades. Unlike radiation, cosmic rays contains very energetic particles such as protons etc. and these particles are very interactive with their surroundings unlike photons. A cosmic ray beam containing such energetic particles can easily change its path by interacting with magnetic or electric fields. Due to this we will get wrong data regarding the actual position of the cosmic ray source. Luckily, these cosmic rays emit radiations while they interact with their surroundings via non- thermal radiative processes and by studying those emitted radiations that we receive on earth we can learn about the original cosmic ray beam. Therefore, studying those radiative processes is a very important part of high energy astrophysics.
The difference between thermal and non-thermal radiative processes is that in the case of a non-thermal radiative process, the characteristics of the emitted radiation do not depend on the temperature of the source. Some of the non-thermal radiative processes is mentioned below-
1) The 21cm radiation due to the Hydrogen spin-flip transition
2) Gamma rays due to nuclear reactions
3) Synchrotron radiation
4) Radiation due to Bremsstrahlung
5) Inverse Compton process
One thing to notice is the fact that it is not necessary that all x-rays and gamma rays that we receive are due to the non-radiative processes. The black body spectrum extends to infinity in terms of frequency, but the energy density becomes very low there. If an object is hot enough, thermal X-rays are still possible. So the deciding factor between thermal and non-thermal is not so much the wavelength of the photon, but its origin.
Therefore, along with the quantitative properties of the high energy radiation that we receive on earth, it is very important to study the qualitative properties of those radiations such as the origin and the process by which that radiation is emitted.
In this project, I have worked on understanding one of such qualitative aspects of high energy radiation. Understanding the origin and predicting few properties such as the power of the radiation by sources such as supernova remnants, pulsars, nebulas etc. is the main motivation behind this project. Synchrotron is one of the main and most common processes by which high energy radiations are emitted by it’s source. Examples of such sources include SNR, AGN, PWN etc. In this project, I have studied the synchrotron emission using basic electromagnetic approach. First I have developed the theory for finding the power emitted by an electron moving in a magnetic field which has both magnitude and direction constant. After this I have extended this theory to include such magnetic fields which have constant magnitude but random directions and finally I have calculated the power per unit frequency of the radiation emitted by electrons moving in a magnetic field which has both non-uniform magnitude and random direction.