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Notes on Sources

Here are some notes about using the gamma-ray sources that are available for use with obsSim.

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The parameter values in params="..." below are as follows: 1. source

1. source flux (photons m ^-2 s ^-1

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1. integrated over [ Emin,Emax ])

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1. photon spectral index for a power-law spectrum

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1. start time (in s)

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1. stop time (in s) for the flare (both measured with respect to whatever the 0 of time is

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1. name of the file that has the flare profile
2. Emin (MeV) for the energy range of the gamma rays
3. Emax (MeV)

NOTE: The last two arguments are optional; the values for the limits default to 30 MeV and 1e5 MeV if not Wiki Markup_NOTE:_ Two other arguments can follow the file name: Emin and Emax (MeV). The gamma rays will be generated within the energy range \[Emin, Emax\]. The values for the limits default to 30 MeV and 1e5 MeV if not specified.

The file (item 5 above) contains two columns, time and flux. They are BOTH
RESCALED; the time column is scaled to match the start and stop times specified in the XML file and the flux entries are scaled so that the MEAN flux is the same as specified in the XML file. transient_profile.dat is available here. The profile rises linearly from 0 for the first 1/3rd of the time, plateaus for the next 1/3rd, and then falls linearly to 0 again in the final 1/3rd of the time interval.

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   <source name="spectral_transient">
      <spectrum escale="MeV">
<!-- 
     mean flux = 0.1 (1e4/m^2/s) integrated over [emin,emax]
     start time = 0 (MET s)
     stop time = 1e4 (MET s)
     template file name = $(GENERICSOURCESROOT)/data/testTemplate.dat
     emin = 20 (MeV, this is the default)
     emax = 2e5 (MeV, default)
     lc # (in FITS file) = 0 (default)
     z (redshift) = 0 (default)
--!>
          <SpectrumClass name="SpectralTransient"
          params="1e-1, 0., 1e4, $(GENERICSOURCESROOT)/data/testTemplate.dat, 20, 2e5, 0, 0"/>
          <celestial_dir ra="193.4" dec="-5.82"/>
      </spectrum>
   </source>

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The parameters in the params="..." attribute are as follows 1.

1. Time of initial GRB (s)

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1. Interval between GRBs (s)

I don't know what the time reference is, i.e., what absolute time 0 corresponds to.

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<source name="Galactic_diffuse">
    <spectrum escale="MeV">
diffuse">
    <spectrum escale="MeV">
        <SpectrumClass name="MapSource"
          params="17.,2.1,$(FLUXROOT)/sources/gas_gal.fits,30.,2e5"/>
         <use_spectrum frame="galaxy"/>
    </spectrum>
</source>

Diffuse interstellar emission with MapCube (Chiang)

The MapCube source is a generalization of the MapSource source. MapCube allows separate maps to be specified for arbitrary energies. This allows for spectral variations across a diffuse source. I think that in generating gamma rays, MapCube interpolates in log(Energy) between the planes.

MapCube was used to generate the interstellar gamma rays from the Milky Way for Science Tools Checkout 2 using a cube generated from gamma-ray intensities calculated by GALPROP. Of course, MapCube can be used for sources that don't subtend the entire sky, too.

The MapCube source has only 2 parameters in its specification:

1. Total photon flux from the map, integrated over the energy range of the cube (#/m^2/s)
2. Fits file of cube (plate-carree only)

Note that MapCube requires the input FITS cube to have a binary table extension 'ENERGIES' that defines the energy of each of the spatial planes in the cube.

The FITS cube that I generated from the GALPROP model is available as GP_gamma.fits.gz. (Beware: It is large, ~32 Mbyte uncompressed.) It has dimensions 720x360 (0.5 deg grid spacing in Galactic longitude and latitude) and contains 32 planes spaced by factors of 1.4 in energy, from ~29 MeV to ~980 GeV. This could safely be trimmed to have an upper limit of ~300 GeV, and in fact the calculation probably should not be trusted all the way to 1 TeV.

The units of the FITS cube are differential intensity (e.g., photons cm^-2 s^-1 MeV^1 sr^-1), although the integral value is renormalized by whatever total photon flux is specified in the specification of the source.

Note that GP_gamma.fits does not contain extragalactic diffuse emission. See notes above for MapSource and below for an isotropic emission source.

The example below is for the GP_gamma.fits model of the interstellar emission of the Milky Way.

   <source name="GALPROP_source">
      <spectrum escale="MeV">
<!-- Total photon flux from the map (#/m^2/s) = 12.59
     Fits file (plate-carree only)=/a/surrey01/vol/vol2/g.glast_users/glground/d
igel/galprop/GP_gamma.fits-->
         <SpectrumClass name="MapSourceMapCube"
          params="1712.,2.1,$(FLUXROOT)/sources/gas_gal.fits,30.,2e559,GP_gamma.fits"/>
         <use_spectrum frame="galaxy"/>
      </spectrum>
   </source>
</source_library>

Isotropic emission as a source in instrument coordinates (who wrote it?)

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