Sources Available to gtobssim and Gleam

In addition to sources already available from the flux package (e.g., constant point sources with power-law or broken power-law spectra, isotropic diffuse, MapSpectrum's Galactic diffuse), there are several sources that are available to gtobssim and Gleam through the celestialSources container package. Here we document the sources available in the genericSources subpackage. These sources derive from the Spectrum class of the flux package, and accordingly, their xml entries all have the same form. The params string provides a means of circumventing the DTD, and thereby allows essentially free-format data to be passed to the Spectrum class.

In the examples below, the parameter escale specifies the units of energy used elsewhere in the source specification. It can have values MeV or GeV, and defaults to GeV.

Notice that coordinates can be specified either as celestial (J2000) or Galactic. For example:

<celestial_dir ra="123.45" dec="67.8"/> or <galactic_dir l="23.45" b="-67.8"/>

CAUTION:  Avoid using source names starting with "J###" where # is 0-9.  The XML parser currently has a bug that makes it misinterpret the names.

For each source, the entries in the param string are described.

Notes:

1. The XML tag <use_spectrum frame="galaxy"/> indicates to the Gleam code
   that the photons are to be generated in Celestial coordinates as opposed to instrument coordinates.  Its use in these XML definitions is idiomatic and specific to particular source implementations and generally applies to diffuse sources only. Ppint sources should not use this tag; use celestial_dir or galactic_dir instead.

2. Optional parameter default values are given in parentheses.

• Gamma-ray point source: A point source with a steady light curve.

In this example, a monochromatic (110 GeV) point source with flux 5e-4 m-2 s-1 is placed in the direction of the Galactic center:

     <source name="galcenter" flux="5e-4">
          <spectrum escale="GeV">
          <particle name="gamma">
              <energy e="110."/>
          </particle>
          <galactic_dir l="0" b="0"/>
          </spectrum>
          </source>

In this example, a source with a power-law spectrum with photon spectral index 1.62 and flux 0.00928 m-2 s-1 between 30 MeV and 100 GeV is placed at RA 128.73, Dec -45.2.  Note that "gamma" is used both to indicate the particle type and to denote the spectral index.

     <source name="vela" flux="0.00928">
          <spectrum escale="MeV">
          <particle name="gamma">
              <power_law emin="30.0" emax="100000." gamma="1.62"/>
          </particle>
          <celestial_dir ra="128.73" dec="-45.2"/>
          </spectrum>
          </source>
          

In this example, the source above is modified to have a broken power-law spectrum, with break energy ebreak and spectral index gamma2 above the break:

• GaussianSource:  Incident photons are distributed as a 2D Gaussian projected on the sky. A 2D Gaussian is defined as a one dimensional Gaussian distribution in the major axis times a one dimensional Gaussian distribution in the minor axis.

• flux Total flux in units of .
• gamma Photon spectral index such that .
• RA Source centroid J2000 right ascension in degrees.
• Dec Source centroid J2000 declination in degrees.
• major axis (default: 1)The Gaussian width (sigma) of the one dimensional Gaussian distribution along the major axis. This means that 68% of the photons will be within one sigma on either side of mean value along the major axis (integrated over the minor axis).
  
• minor axis (default: 1) Gaussian width (sigma) of the one dimensional Gaussian distribution along the minor axis.
  
• position angle (default: 0) Position angle of the major axis measured wrt North in degrees.
  
• Emin (default: 30) Minimum photon energy in MeV.
• Emax (default: 1e5) Maximum photon energy in MeV.
  

     <source name="gaussian_source">
        <spectrum escale="MeV">
           <SpectrumClass name="GaussianSource"
               params="0.1, 2.1, 45., 30., 3., 0.5, 45, 30., 2e5"/>
           <use_spectrum frame="galaxy"/>
        </spectrum>
     </source> 

• FileSpectrum: Spectrum defining a source for which the energy distribution is determined by a 2 column ascii file. The first column contains the energies, and second column contains the differential flux at those energies. The units of energy in the first column should match the escale attribute that is set in the spectrum tag. Do not set the flux attribute in the spectrum tag, otherwise the fluxes for this source will not be correct. To be explicit, a spectrum tag that looks like this

  <spectrum escale="MeV" flux="1">

  is not correct, whereas

  <spectrum escale="MeV">

  is ok.

• flux Total flux of the source. This acts as a normalization of the spectrum. If this attribute is set to zero, i.e., flux="0", then the spectrum data in the file will be integrated and that integral will be used as the source flux. The units are assumed to be .
• specFile Name (and path) to the ascii file The position of the source is determined in the usual way, in the XML definition.
  

• TF1Spectrum: Spectrum defining the a source for which the energy distribution is determined by a symbolic expression. This expression is parsed and managed via a ROOT TF1 instance.

• formula The symbolic formula to be used, for instance exp(-x).
• tf1name Unique name to identify the TF1 object in ROOT internal memory.
• tf1precision (default: 30) Determines the number of points ROOT is going to use in order to approximate the function.
• flux Total flux of the source (act as a normalization of the equation).
• emin Minimum energy.
• emax Maximum energy.
  

Note: The position of the source is determined in the usual way in the XML definition.

• Isotropic: Photons are generated uniformly on the sky following a power-law spectrum. A sky-cone selection on the generated photons may be applied. The flux is integrated over the specified energy range and emin and emax must be given.

• flux in units of .
• gamma Photon spectral index such that .
• emin Minimum photon energy in MeV.
• emax Maximum photon energy in MeV.
• ra (default: 0) RA of sky-cone center in J2000 degrees.
• dec (default: 0) Dec of sky-cone center in J2000 degrees.
• radius(default: 180) Radius of sky-cone in degrees.

     <source name="Extragalactic_diffuse">
        <spectrum escale="MeV">
           <SpectrumClass name="Isotropic"
                          params="flux=10.7,gamma=2.1,emin=20.,emax=2e5,ra=0,dec=0,radius=180"/>
           <use_spectrum frame="galaxy"/>
        </spectrum>
     </source>       

• MapCube: Incident photons are generated from a 3D FITS image comprising an energy axis for the 3rd dimension and, e.g., RA and Dec as the sky coordinates. The pixel values in each image should have dimensions of . The absolute normalization is not important as the image will be rescaled by the flux parameter. The energies corresponding to each image frame must be given in binary table extension. Here is an example FITS file, and here is a thorough treatment of Celestial coordinate projections for FITS images.

• flux Total flux from the map, integrated over solid angle, in units of .
• FITS file A plate-carree FITS image in Galactic '(CTYPE1 = GLON-CAR, CTYPE2 = GLAT-CAR)' or J2000 '(CTYPE1 = RA---CAR, CTYPE2 = DEC--CAR)' coordinates.

     <source name="map_cube_source">
        <spectrum escale="MeV">
           <SpectrumClass name="MapCube"
               params="1., $(GENERICSOURCESROOT)/data/test_image.fits"/>
           <use_spectrum frame="galaxy"/>
        </spectrum>
     </source>          

• MapSource: Photons are generated using a 2D FITS image as a template. A single power-law spectrum is used for the entire map.
  
  
  • flux Total flux from the map, integrated over solid angle, in units of .
  • gamma Photon spectral index such that .
  • FITS file A plate-carree FITS image in Galactic '(CTYPE1 = GLON-CAR, CTYPE2 = GLAT-CAR)' or J2000 '(CTYPE1 = RA---CAR, CTYPE2 = DEC--CAR)' coordinates.
  • Emin (default: 30) Minimum photon energy in MeV.
  • Emax (default: 1e5) Maximum photon energy in MeV.

     <!-- MapSource version of the Galactic Diffuse model -->
       <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>                        

• FileSpectrumMap: Same as File Spectrum, but now the source can be extended in space.

• All the parameters of FileSpectrum.
• All the parameters of MapSource.

   <source name="filespectrummap_test">
     <spectrum escale="GeV" flux="1.">
       <SpectrumClass name="FileSpectrumMap"
         params="flux=17.,fitsFile=$(FLUXROOT)/sources/gas_gal.fits,
         specFile=$(GENERICSOURCESROOT)/data/dm120gev.dat,emin=100.,emax=1100,
         tf1precision=100,gamma=2,lonMin=-180,lonMax=180,latMin=-90,latMax=90"/>
       <use_spectrum frame="galaxy"/>
     </spectrum>
   </source>

• TF1Map: Same as 3) but now the source can be extended in space.

• All the parameters of TF1Spectrum.
• All the parameters of MapSource.

• PeriodicSource: A point source with sinusoidal light curve.
  
  

• flux Average flux in units of .
• gamma Photon spectral index such that .
• period Source period in seconds.
• amplitude (default: 0.5) Amplitude of the sinusoidal modulation.
• phi0 (default: 0) Phase offset specified on the unit interval.
• Emin (default: 30) Minimum photon energy in MeV.
• Emax (default: 1e5) Maximum photon energy in MeV.

     <source name="periodic_source">
        <spectrum escale="MeV">
           <SpectrumClass name="PeriodicSource"
                     params="0.1, 2.1, 1e3, 1, 0.75, 30., 2e5"/>
           <galactic_dir l="0" b="0"/>
        </spectrum>
     </source>

• GRBobs

  Note: The GRBobs package is a redefinition of the GRB phenomenological model for Gamma-Ray Bursts, using the same schema as the GRB physical model (GRB package) but, instead of exploring the physics for deriving light curves and the spectra, it uses phenomenological prescriptions.

The xml spectrum object has to be defined as follows:

where the params are:

• Starting time of the burst (s)
• Fluence in . If it is 0 then it has sampled from the BATSE fluence distribution.
• The number of pulses of the bursts.
• The low energy spectral index ()
• The high energy spectral index ()
• The minimim energy for extracting photons (in MeV).
• The flag for the GBM output. (1==YES and 0=NO). If GBM output is generated, the sumulator is slower and an additional text file will be created (see, GRBobsSim::SaveGBMDefinition and GRBobsSim::GetGBMFlux)

Also see:

• GRBobs Package: phenomenological model for GRB
• Gamma-Ray Burst @ Pisa

• Pulsar: A pulsar source whose light curve is given by an ascii template file.

• flux Average flux in units of .
• gamma Photon spectral index such that .
• period Pulsar period in seconds.
• pdot Time derivative of the pulsar period in .
• t0 Reference epoch in MET seconds.
• template file Filename of the ascii light curve template. The file should consist of two columns, phase and intensity. The phase intervals must be uniformly spaced. The phase scale and absolute intensities are arbitrary and rescaled using the period and flux parameter values.
• phi0 (default: 0) Phase offset in the unit interval.
• Emin (default: 30) Minimum photon energy in MeV.
• Emax (default: 1e5) Maximum photon energy in MeV.

• SimpleTransient: A point source with a single active interval during which it has a constant flux and power-law spectrum.
  
  
  • flux Flux while in the active state in units of .
  • gamma Photon spectral index such that .
  • tstart Start time of the active state in MET seconds.
  • tstop Stop time of the active state in MET seconds.
  • Emin Minimum photon energy in MeV. (default = 30)
  • Emax Maximum photon energy in MeV. (default = 1e5)

     <source name="simple_transient">
        <spectrum escale="MeV">
           <SpectrumClass name="SimpleTransient"
            params="10., 2., 1e3, 1.1e3, 30., 2e5"/>
           <celestial_dir ra="83." dec="22."/>
        </spectrum>
     </source>

• SpectralTransient: An ascii or FITS file containing the light curve data is used as a
  template. Here are example ascii  and FITS files.
  
  
  • flux Mean flux during the active state in units of .
  • tstart Start time of the active state in MET seconds.
  • tstop Stop time of the active state in MET seconds.
  • template file Filename of the light curve template. May be ascii or FITS.
  • Emin (default: 20) Minimum photon energy in MeV.
  • Emax (default: 2e5)Maximum photon energy in MeV.
  • lc (default: 0) light curve number, if FITS file.
  • z (default: 0) Redshift used for EBL attenuation calculation.
  • useLogParabola (default = 0)

     <source name="spectral_transient">
        <spectrum escale="MeV">
            <SpectrumClass name="SpectralTransient"
            params="flux=1e-1, tstart=0., tstop=1e4, 
            templateFile=$(GENERICSOURCESROOT)/data/testTemplate.dat, 
            emin=20, emax=2e5, lc=0, z=0, useLogParabola=0"/>
            <celestial_dir ra="193.4" dec="-5.82"/>
        </spectrum>
     </source>

• TransientTemplate: A point source transient whose active state light curve shape
  is given by an ascii template file.
  
  
  • flux Mean flux during the active state in units of .
  • gamma Photon spectral index such that .
  • tstart Start time of the active state in MET seconds.
  • tstop Stop time of the active state in MET seconds.
  • template file Filename of the ascii light curve template. The file should consist
    of two columns, time and intensity. The time intervals must be uniformly spaced.
    The time scale and absolute intensities are arbitrary and rescaled using the flux,
    tstop, and tstep parameter values.
  • Emin (default: 30) Minimum photon energy in MeV.
  • Emax (default: 1e5) Maximum photon energy in MeV.

      <source name="transient_template">
        <spectrum escale="MeV">
          <SpectrumClass name="TransientTemplate"
             params="100.,2,1e3,1.1e3,$(OBSERVATIONSIMROOT)/data/CrabTemplate.dat"/>
          <celestial_dir ra="80" dec="20"/>
        </spectrum>
      </source>
     

• RadialSource: An extended source with a radial profile given by an ascii template file.
  
  
  • flux Source flux in units of .
  • profileFile An ASCII file containing the radial profile of the source on the sky. The columns should be degrees and flux per steradian. Note that the total source flux will be rescaled according to the value of the flux parameter.
  • specFile An ASCII file containing the spectrum of the source. The columns should be degrees and differential photon flux (e.g., photon/cm^2/s/MeV). A power-law is used to interpolate between energies so logarithmic spacing of the abscissa points should be used. Again, note that the total source flux will be rescaled according to the value of the flux parameter.
  • ra Right ascension of the center of the source (J2000 degrees)
  • dec Declination of the center of the source (J2000 degrees)