Where can I set target gas density parameter?

[skumarudel]

Hi, I was looking into the code and unable to find where can i put the parameter for the gas density with which cosmic ray will interact? For example lets say i want to use 30 cm^-3 as the cloud density to model gamma-ray emission.

Thank you, Sajan

[skoldobskiy]

Dear Sajan, thank you for noticing that issue, which was described in very small detail in the Jupyter Notebook. The integral calculated in the example is: $$\int{0}^{+\infty} n\text{gas} \frac{dJ\text{CR}}{dE\text{CR}} \frac{d\sigma}{dE}dE\text{CR}$$ where $n\text{gas}$ = 1 cm^-3. You can substitute the needed value (basically, it is just a multiplier) if you want to calculate the gamma-ray flux for the cloud.

I will add a more detailed description of that in the Jupyter Notebook file later.

[skumarudel]

Thank you a lot! I will look at the notebook once it is uploaded. In terms of units (cm-3) (1 / GeV) (cm2 / GeV) (GeV) = 1 / GeV / cm Should it not gives us number of particles per unit energy which is 1 / GeV ---> (1 / GeV / sec). I do not know this extra cm. May be I am missing something here. Then I can divide this by distance of source (4 pi * distance^2) which gives 1 / GeV / cm2 (this will be measure gamma ray flux).

[skumarudel]

I think I miss to multiply by "c" which will change the units to (u.cm*-3) (u.cm*2 / u.GeV) (u.GeV) (1 / u.GeV) (u.cm / u.second) = 1 / GeV / sec and when I divide this by distance square it will give me flux in unit of (GeV-1 cm-2 s-1)

[skoldobskiy]

It depends on what you are trying to calculate. Probably, the thing you want to calculate is the line-of-sight integral. It allows you to calculate the observable gamma-ray flux on Earth considering the gamma-ray source (gas+cosmic rays) somewhere else. The equation looks like this: $$\frac{dJ_i}{dEi} = \int{r_1}^{r2} \int{\phi_1}^{\phi2} \int{\theta_1}^{\theta2} n\mathrm{gas}(r,\phi,\theta) \left[ \sum_{i,j} \int_0^\infty \frac{dJi}{dE} \frac{d\sigma{A{i} A{j} \rightarrow \nu_{\mu}}}{dE} (r,\theta,\phi) dE_i \right] \sin (\theta) dr d\phi d\theta$$

Note that:

1. Something-pi multiplier is probably missing.
2. Division by distance^2 will be diminished by multiplication by distance^2 because of widening the line-of-sight.
3. Any gamma-ray fluxes are subject to the absorption process.

[skumarudel]

Thank you a lot! Yes I am interested in calculated gamma-ray flux on earth. I will really appreciate if you can upload a notebook on git with a simple example how to calculate gamma-ray flux on earth (if it is not a too much work). that way I will be more confident that whatever, I am doing is correct.

[skoldobskiy]

Sorry, but just right now, I don't have a solution for you. I am working on a simple Python-based LOS integrator, but it is still not ready. I can notify you if it will be produced soon. In the meantime, you can also try other codes that can do this kind of computation, such as HERMES (https://github.com/cosmicrays/hermes).