Fermi Gamma-ray Space Telescope

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Simple Models

XML is not meant for human eyes. Software is supposed to read and write these files, insulating the human from all the '<' and '>' symbols. However, an example of the XML file for a simple point source might assist you in understanding the XML model files that are used for simulations. And if you want to change one parameter in a model file, you might venture where no human is meant to, and edit the XML file directly with an ASCII editor.

The following is the model for a point source:

<source_library title="example_3C279"> <source name="_3C279" flux="3.48e-4"> <spectrum escale="MeV"> <particle name="gamma"> <power_law emin="20.0" emax="200000." gamma="1.96"/> </particle> <celestial_dir ra="193.98" dec="-5.82"/> </spectrum> </source> </source_library>

Clearly, the point source is supposed to model 3C279 and is located at (Ra=193.98, Dec=-5.82). The spectrum is a power law with a photon spectral index of 1.96 and an integrated flux of 3.48e-4 m-2s-1 over 20 to 20,000 MeV. Note that all the spectral parameters are in one tag. Because this XML format is also used within the Fermi mission to model non-photon fluxes impinging on the LAT, the particle type is given as 'photon' (which will always be the case for simulating astrophysical sources)

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