cdeil
commented
6 years ago @GernotMaier - The difference in the equations you give is just whether they contain e_cut or lambda=1/e_cut, right?
In gamma-cat we currently use e_cut.
You can see this in the schema: https://github.com/gammapy/gamma-cat/blob/aa4aa0922559b43d602ce06eafeb4ccd222aeb7b/input/schemas/dataset_source_info.schema.yaml#L325 and how the catalog is filled: https://github.com/gammapy/gamma-cat/blob/ba11b084a1342d64ca80c35a8b46da2f59f20889/gammacat/catalog.py#L325
Indeed when we map to a spectral model in Gammapy
https://github.com/gammapy/gammapy/blob/f48b22d7f7ab9430bb2ab78521736a6e381b5318/gammapy/catalog/gammacat.py#L271
we use
http://docs.gammapy.org/dev/api/gammapy.spectrum.models.ExponentialCutoffPowerLaw.html which has lambda, but that is filled as lambda=1/e_cut.
Note that if needed, we can add more spectral models to gamma-cat and Gammapy. E.g. in Gammapy we already have this second ECPL parametrisation because it was used in the Fermi-LAT 3FGL catalog: http://docs.gammapy.org/dev/api/gammapy.spectrum.models.ExponentialCutoffPowerLaw3FGL.html
@GernotMaier - So is there an issue with the data entry for VERITAS?
The HESS catalog will come out soon and I want to add the data to gamma-cat. There we use lambda and lambda_err. So I guess we should add an ECPL variant to gamma-cat that supports direct data entry of lambda and lambda_err, no? Any suggestion for what to call it? I think in HESS this is "ecpl3". :-)
GernotMaier
Noticed right that the definition of the power law with exponential cut off is different than expected. Can you please confirm?
I've expected: dN/dE = I0 · (E/E_ref)−Γ · exp(−E/Ecut)
Looks like the implementation is dN/dE = I0 · (E/E_ref)−Γ · exp(−E*lambda)
If this is true, all ecpl in the VERITAS files need to be adjusted. I will do this, but please confirm that the second implementation is the one used.