Introduction

This study is intended to address concerns raised by Stefan in his energy dispersion studies and results for the region containing IC443 (and W44).

The input simulations.

The model includes Galactic diffuse, isotropic diffuse, and IC443:

For simulation purposes, a FileSpectrum template was used.

High flux versions of these sources were simulated on a 1-day observation time using idealized +/- 50 degree rocking:

<source name="Galactic_Diffuse_ext">
  <spectrum escale="MeV">
    <SpectrumClass name="MapCube"
        params="1e3, galdif_extended.fits"/>
    <use_spectrum frame="galaxy"/>
  </spectrum>
</source>
<source name="Isotropic_Diffuse">
  <spectrum escale="MeV">
    <SpectrumClass name="IsotropicFileSpectrum"
        params="flux=800, specFile=iso_p7v6source_extrapolated.txt"/>
     <use_spectrum frame="galaxy"/>
  </spectrum>
</source>
<source name="IC443">
  <spectrum escale="MeV">
    <SpectrumClass name="FileSpectrumMap" 
        params="flux=10.,fitsFile=IC443.fits,specFile=IC443_sbpl.txt,emin=10,emax=1e6"/>
    <use_spectrum frame="galaxy"/>
  </spectrum>
</source>

This yields ratios of numbers of events within a nominal 14 degree radius cone about IC 443 of Galactic:Isotropic:IC443 = 10:1:10 for the energy range 20-5000 MeV.

Binned Analysis

The likelihood xml-model definition

<?xml version="1.0" standalone="no"?>
<source_library title="source library">
  <source name="IC443" type="DiffuseSource">
    <spectrum type="SmoothBrokenPowerLaw">
      <parameter error="0.4954398855" free="1" max="100" min="0.01" name="Prefactor" scale="1e-6" value="1" />
      <parameter error="0.1215327591" free="1" max="5" min="-5" name="Index1" scale="1" value="-0.5" />
      <parameter free="0" max="200" min="200" name="Scale" scale="1" value="200" />
      <parameter error="0.02281532475" free="1" max="5" min="-5" name="Index2" scale="1" value="-1.9" />
      <parameter error="21.72157285" free="1" max="1000" min="100" name="BreakValue" scale="1" value="250" />
      <parameter free="0" max="0.1" min="0.1" name="Beta" scale="1" value="0.1" />
    </spectrum>
    <spatialModel file="IC443.fits" type="SpatialMap">
      <parameter free="0" max="1000" min="0.001" name="Prefactor" scale="1" value="1" />
    </spatialModel>
  </source>
  <source name="Galactic Diffuse" type="DiffuseSource">
    <spectrum type="PowerLaw">
      <parameter error="0.002799883743" free="1" max="1e4" min="0." name="Prefactor" scale="1" value="50" />
      <parameter error="0.003039083563" free="1" max="1" min="-1" name="Index" scale="-1" value="0.0" />
      <parameter free="0" max="1000" min="1000" name="Scale" scale="1" value="1000" />
    </spectrum>
    <spatialModel file="galdif_extended.fits" type="MapCubeFunction">
      <parameter free="0" max="1000" min="0.001" name="Normalization" scale="1" value="1" />
    </spatialModel>
  </source>
  <source name="Isotropic Diffuse" type="DiffuseSource">
    <spectrum file="iso_p7v6source_extrapolated.txt" type="FileFunction">
      <parameter error="0.01269613352" free="1" max="1e4" min="0" name="Normalization" scale="1" value="10." />
    </spectrum>
    <spatialModel type="ConstantValue">
      <parameter free="0" max="10" min="0" name="Value" scale="1" value="1" />
    </spatialModel>
  </source>
</source_library>

The data were analyzed for three subselections, with counts cubes generated for emin, emax = 20, 5000 MeV (30 energy bands) for a 10x10 deg region centered on IC443:

  1. IC443 events only
  2. IC443 + Galactic + Isotropic (at full simulated statistics)
  3. IC443 decimated by a factor of 10 + Galactic + Isotropic such that Galactic:Isotropic:IC443 = 10:1:1

The selected energy range for fitting was emin, emax = 60, 2000 MeV using 

>>> like.setEnergyRange(60, 2000)

These three cases were analyzed both with energy dispersion handling turned off and turned on.

Results