I recently noticed that electron inverse Compton energy losses are treated in the Thompson limit using the total ISRF energy density.
In my original development of the code around 2000 this was done as a provisional solution with the idea to upgrade this but somehow it got forgotten.
It means the energy losses at high energies (TeV) on optical radiation fields are incorrect as it enters the Klein-Nishina regime.
The correct way to do it is to integrate over the ISRF using the KN formula,
just as is done for gamma-ray production.


Also note that only continuous losses are handled by galprop,
while at high energies the losses become catastropic. This will require
a more fundamental development of the propagation code.

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Andy Strong, MPE

I went and checked this. The KN losses are treated correctly (in create_transport_arrays.cc when electrons/positrons are created, e_KN_loss is called to generate the IC losses for all points in the spatial grid).

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Dr. Troy A. Porter
Hansen Experimental Physics Laboratory
452 Lomita Mall
Stanford University
Stanford, CA 94305

good to know.
In fact it was done by Igor in October 2006
(the other method is still there but only to test analytical cases)




But catastrophic losses are anyway not handled correcly,
a problem at TeV.

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Andy Strong, MPE

Right. To do it properly we would probably need to use a Monte Carlo solution for the transport equations. We could put this in but it would require some redesign (and not just a small amount of it, either).

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Dr. Troy A. Porter
Hansen Experimental Physics Laboratory
452 Lomita Mall
Stanford University
Stanford, CA 94305

The effect of treating this properly is negligible, cf. secondary protons vs primary protons. I did the proper treatment of the catastrophic losses, here is why "secondary protons."

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Igor Moskalenko
Stanford University

Examining the code, I found that right now the energy losses for electrons are treated in the following way:

First of all the method electron_loss(...) gets called, in which the inverse compton losses in the Thompson limit are included.
Later in the code the e_KN_losses(...) function calculates the Klein-Nishina losses. Is it correct to have both methods in the code? Wouldn't energy losses due to inverse compton interactions be considered twice now?

Also, since I am interested in doing calculations with TeV electrons to study the effect of local sources on the spectrum, could you please elaborate on the problem with catastrophic losses?

Cheers
Bastian Beischer

The IC losses are NOT taken into account twice.
Before calling the routine electron_loss, the energy density of photon field is set to zero:
double uevcm3=0.

The effect of catastrophic losses is negligible due to the very steep spectrum of VHE electrons.

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Igor Moskalenko
Stanford University

But the steep spectrum is itself the result of the losses. Maybe it's less steep if they are catastrophic.
Anyway eventually it should be done correctly if we want to do TeV and above.
Meanwhile a simple analytical comparison of the approaches would shed light on the matter.