Difference between thermal and non-thermal Bremsstrahlung

[kop442000]

Can anyone give me a nice explanation of the difference between thermal and non-thermal Bremsstrahlung?

Thank you!

 

[zhermes]

Thermal Bremsstrahlung is generated by particles which obey a thermal (maxwell-boltzmann) distribution. The radiation from the IGM in galaxy clusters is an excellent example.

Non-thermal Bremsstrahlung is just about everything else: e.g. cyclotron/synchrotron radiation in pulsars and quasars.

 

[kop442000]

Thank you I've just seen this reply sorry.

I'm still not sure that I understand. Are you saying that synchrotron radiation for example is non-thermal bremsstrahlung? I thought that bremsstrahlung was when a charged particle was accelerated in the region of a nucleus.

Also, if thermal bremsstrahlung is generated by particles that obey a thermal distribution, why is there no such thing as thermal inverse-compton scattering for example?

Thank you!

 

[Ken G]

The Wiki on brehmsstrahlung says "Strictly speaking, bremsstrahlung refers to any radiation due to the acceleration of a charged particle, which includes synchrotron radiation; however, it is frequently used in the more narrow sense of radiation from electrons stopping in matter." This was my impression also (though I certainly wouldn't have said "stopping", just electons in the fields of ions), so it's kind of a technical detail if we should count synchrotron emission or not.

The essential answer to your question is that thermal vs. nonthermal is not a distinction in the type of process that is making the radiation, it is a distinction in the population of electrons that is undergoing that process, as well as the overall thermal character of all the relevant processes. But typically, bremsstrahlung does refer to radiation made by electrons in the fields of ions. Then if the electrons are "thermalized", then they will have a Maxwell-Boltzmann distribution, as said above, and that means they will make thermal emission, because everything going on is regulated by nothing but the electron distribution, and that has a meaningful temperature and will be the same if it is in thermodynamic equilibrium. Inverse Compton scattering involves something other than the electron distribution, it also depends on the original radiation field, so that would only be thermal if the initial radiation field was thermalized and at the same T as the electrons. Emission like that wouldn't do anything, as the radiation field was already thermal, so would hardly get mentioned. Plus, it doesn't really get called inverse Compton unless the electrons are relativistic, and thermal relativistic environments are not terribly common, but it might be fair to say that thermal inverse Compton scattering occurs copiously in the core of a supernova.