Page History

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FT1 event files generated for these sources used an FT2 file for a one-week scanning/rocking observation. These files are available here. For all of these FT1 files, I used the random seed 34621 in obsSim.par. There's nothing special about this number, but don't be surprised when you get different gamma rays if you use a different seed. All FT1 files are for the FRONT/BACK (i.e., DC1) response functions.

I can't personally vouch for the correctness of the output for any of these sources. I haven't seen anything that looks obviously wrong yet, but I haven't tried quantitatively studying the numbers of gamma rays that the source sources generate and I haven't seriously tried any timing studies.

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Here is the distribution of the events on the sky (with some outliers cropped off) for this simulation. Also shown is the overall counts spectrum for the one-week observation.

Note: This source apparently also leaves behind a file called pulsar.root in the directory from which you run obsSim.

GalPulsars (Hierath)

There's nothing really to specify in the XML file. All of the information is in the file named in the params attribute, which is human readable. The file flux/v8r10p2/sources/pulsars.txt has many more pulsars.

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Note: I do not know right now why this source generated so many fewer gamma rays than the one above (470 vs. 1842). Nominally Vela is brighter. I used the source specifications exactly as they were given in the XML files in the repository.

GRBmanager (Omodei & Cohen-Tanugi?)

The source below is mostly lifted from celestialSources/GRB/v4r0p7/xml/GRB_user_library

The parameters in the params="..." attribute are as follows
1. Time of initial GRB (s)
2. Interval between GRBs (s)

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

Nothing else other than the coordinates of the GRB can be specified. You must be careful to have the GRBs go off when they are in the FOV of the LAT. One unphysical way to do this (pointed out to me by Johann) is to replace the galactic_dir line with, e.g., <direction frame="glast" theta="0" phi="0"/>, which fixes the GRB to be right on the LAT z-axis no matter where it is pointed.

Note: this source will also make grb_#####.root files in your current directory. These files are alleged to contain 2-dim histograms of the GRB and are generated whether or not the GRB was within the FOV. -->

<source name="GRB_50_60">
    <spectrum escale="MeV"> <SpectrumClass name="GRBmanager" params="10000
,20000"/>
        <galactic_dir l="50" b="60"/>
    </spectrum>
</source>

Here are the times and energies of the 104 gamma rays that this source generated for the one week observation period. The second plot is the time history of the gamma rays in the intense burst near the end of the week.

Image Added

Diffuse interstellar emission with MapSource (Chiang?)

The source below is lifted from observationsSim/v5r1p3/xml/obsSim_source_library.xml

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The 'MapSpectrum' source can also be used for this purpose. I don't know whether one is superior to the other. The definitions of the params="..." attributes are given below:

1. Total photon flux from the map (#/m^2/s) = 17.
2. Photon spectral index = 2.1
3. Fits file (plate-carree only) = $(FLUXROOT)/sources/gas_gal.fits
4. Minimum photon energy (MeV) = 30.
5. Maximum photon energy (MeV) = 2e5

gas_gal.fits is the EGRET team's interstellar emission model (basically Hunter et al. 1997). The file is a 2-dimensional array of the integrated intensity (>100 MeV) on a 30' grid in Galactic coordinates. For MapSource there's nothing special about the grid size, or using Galactic vs. celestial coordinates. The important point is that the image be in a flat (plate-caree) projection, as mentioned above.

This source generated 502320 gamma rays for the run that I made. In obsSim.par, I had set a limit of 200k events per output FITS file, so the output spans 3 FITS files.

Note that gas_gal.fits does not contain extragalactic diffuse emission. This was determined with EGRET to have an isotropic distribution with integrated intensity 1.5 x 10 ^-5 cm ^-2 s ^-1 sr ^-1 (>100 MeV, Sreekumar et al. 1998). The expectation is that the LAT will resolve a significant fraction of this into point sources (blazars). Still, the isotropic intensity or its equivalent in point sources should be included in the model for realistic representation of the celestial gamma-ray background. You can do this either by adding a constant intensity to gas_gal.fits and writing it out in a new FITS file, or you can define an additional, isotropic source for obsSim.

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

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

This source is actually defined in terms of cos(theta), i.e., with respect to the instrument axis rather than in some celestial system. You can get away with this for an isotropic celestial source. I assume that occultation by the earth is properly taken into account, although it hardly matters for the step-rocking observation strategy. Occultation of this source would be worth checking, though, for a pointed observation.

The source below implements the extragalactic diffuse inferred by EGRET (Sreekumar et al. 1998). The flux has units of photons m ^-2 s ^-1 integrated between Emin and Emax. The photon spectral index is gamma, i.e., dN/dE = Const*E ^-gamma .

    <source name="extragalactic" flux="0.545">
       <spectrum escale="MeV">
          <particle name="gamma">
             <power_law emin="30." emax="100000." gamma="2.1"/>
          </particle>
          <solid_angle mincos="-0.4" maxcos="1."/>
       </spectrum>
    </source>

This source generated 163,716 gamma rays in the one-week observation.

More sources to come